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NCERT Solutions for Class 8 Maths Chapter 7 Proportional Reasoning 1 (PDF) – 2027

NCERT Solutions for Class 8 Maths Chapter 7 Proportional Reasoning 1 – step-by-step answers to every exercise and in-text question of the chapter, as per the latest NCERT syllabus for 2027. Read them online or download the free question-answer PDF.

Chapter 7 closes Ganita Prakash Part I. It opens with five resized copies of the same photograph of a tiger and asks a question you can answer by eye but not yet by arithmetic — why do three of them look right and two look stretched? The answer is the ratio: a shape survives resizing only when every measurement is multiplied by the same factor. From that one idea the chapter builds proportion, cross multiplication, the ancient Trairasika (Rule of Three), sharing a quantity in a given ratio, and unit conversion.

NCERT Solutions for Class 8 Maths Chapter 7 Proportional Reasoning 1 PDF

All the answers are on this page below. The PDF also explains every answer – why it is right and how to check it – so download it for revision.

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Solutions PDF (English medium)Proportional Reasoning 1View PDF
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NCERT Solutions for Class 8 Maths Chapter 7 Proportional Reasoning 1 – Questions and Answers

All 69 questions of the chapter (textbook pages 159 – 177) are answered below, in the order of the book – in-text questions, activities and the end-of-chapter exercises. Each answer is written the way you would write it in the exam.

In-text Questions — Pages 159–1607.1 Observing Similarity in Change

Math Talk
Q1Which images look similar and which ones look different?
tigerImage AtigerImage BtigerImage CtigerImage DtigerImage E
The five images on page 159. Each frame holds the same photograph of a walking tiger, resized; the frames are drawn here with the widths and heights the book gives for them (described here; see the textbook for the photograph).
Answer

Images A, C and D look similar. Images B and E look different — even though every one of the five shows the same tiger.

A → 60 mm × 40 mm → 3 : 2
C → 30 mm × 20 mm → 3 : 2
D → 90 mm × 60 mm → 3 : 2
B → 40 mm × 20 mm → 2 : 1
E → 60 mm × 60 mm → 1 : 1
Q2Do images B and E look like the other three images?
tigerImage AtigerImage BtigerImage CtigerImage DtigerImage E
The five images on page 159. Each frame holds the same photograph of a walking tiger, resized; the frames are drawn here with the widths and heights the book gives for them (described here; see the textbook for the photograph).
Answer

No. They are distorted. In B the tiger appears stretched and elongated; in E it appears compressed and fatter.

B → 40 : 20 = 2 : 1 (wider than 3 : 2 for its height)
E → 60 : 60 = 1 : 1 (not wide enough for its height)
Q3Why?
Answer

Because in B and E the width and the height were not changed by the same factor.

A → B : width 60 → 40, factor 40⁄60 = 2⁄3 ; height 40 → 20, factor 20⁄40 = 1⁄2
A → E : width 60 → 60, factor 1 ; height 40 → 60, factor 60⁄40 = 3⁄2

In each case the two factors are different, so one direction was stretched more than the other.

Q4What makes images A, C, and D appear similar, and B and E different?
ImageWidth (in mm)Height (in mm)
Image A6040
Image B4020
Image C3020
Image D9060
Image E6060
The table on page 160: the width and height of each image.
Answer

A, C and D were obtained from one another by multiplying both the width and the height by the same factor. B and E were not.

From A toWidth factorHeight factorSame?
C (30 × 20)30⁄60 = 1⁄220⁄40 = 1⁄2Yes — similar
D (90 × 60)90⁄60 = 3⁄260⁄40 = 3⁄2Yes — similar
B (40 × 20)40⁄60 = 2⁄320⁄40 = 1⁄2No — distorted
E (60 × 60)60⁄60 = 160⁄40 = 3⁄2No — distorted
Q5Can you check by what factors the width and height of image D change as compared to image A? Are the factors the same?
ImageWidth (in mm)Height (in mm)
Image A6040
Image B4020
Image C3020
Image D9060
Image E6060
The table on page 160: the width and height of each image.
Answer

Both factors are 3⁄2, so yes, they are the same.

Width: 60 × f = 90 ⇒ f = 90⁄60 = 3⁄2
Height: 40 × f = 60 ⇒ f = 60⁄40 = 3⁄2

In-text Questions — Page 1617.2 Ratios · 7.3 Ratios in their Simplest Form

Q1By what factor should we multiply the ratio 60 : 40 (image A) to get 90 : 60 (image D)?
Answer

By the factor 3⁄2, applied to both terms.

60 × 3⁄2 : 40 × 3⁄2
= 90 : 60
Q2What is the simplest form of the ratios of images B and E?
ImageWidth (in mm)Height (in mm)
Image A6040
Image B4020
Image C3020
Image D9060
Image E6060
The table on page 160: the width and height of each image.
Answer

Divide each pair of terms by their HCF.

Image B: 40 : 20, HCF = 20 → 40⁄20 : 20⁄20 = 2 : 1
Image E: 60 : 60, HCF = 60 → 60⁄60 : 60⁄60 = 1 : 1

Neither of these is 3 : 2, so the ratios of B and E are not proportional to those of A, C and D — which is the arithmetic behind what your eye already noticed.

In-text Questions — Pages 162–1637.4 Problem Solving with Proportional Reasoning (Examples 1–5)

Math Talk
Q1Example 1: Are the ratios 3 : 4 and 72 : 96 proportional?
Answer

Yes. Both have the same simplest form.

3 : 4 is already simplest (HCF of 3 and 4 is 1)
72 : 96, HCF = 24 → 72⁄24 : 96⁄24 = 3 : 4
So 3 : 4 :: 72 : 96
Q2What is the HCF of 72 and 96?
Answer

24.

72 = 2 × 2 × 2 × 3 × 3 = 2³ × 3²
96 = 2 × 2 × 2 × 2 × 2 × 3 = 2⁵ × 3
Common part = 2³ × 3 = 24

Dividing both terms of 72 : 96 by 24 gives 3 : 4.

Q3Example 2: Kesang wanted to make lemonade for a celebration. She made 6 glasses of lemonade in a vessel and added 10 spoons of sugar to the drink. Her father expected more people to join the celebration. So he asked her to make 18 more glasses of lemonade. To make the lemonade with the same sweetness, how many spoons of sugar should she add?
Answer

30 spoons of sugar for the 18 extra glasses.

glasses : spoons must stay proportional
6 : 10 :: 18 : ?
First term: 6 → 18, factor = 18 ÷ 6 = 3
Second term must change by 3 as well: 10 × 3 = 30
6 : 10 :: 18 : 30
Q4How can we find the factor of change in the ratio?
Answer

Divide the new term by the old term of the same quantity.

factor = new first term ÷ old first term
= 18 ÷ 6 = 3
Q5Example 3: Nitin and Hari were constructing a compound wall around their house. Nitin was building the longer side, 60 ft in length, and Hari was building the shorter side, 40 ft in length. Nitin used 3 bags of cement but Hari used only 2 bags of cement. Nitin was worried that the wall Hari built would not be as strong as the wall he built because she used less cement. Is Nitin correct in his thinking?
Answer

No, Nitin is not correct. The two walls are equally strong.

Nitin: length : bags = 60 : 3, HCF = 3 → 20 : 1
Hari: length : bags = 40 : 2, HCF = 2 → 20 : 1
60 : 3 :: 40 : 2
Q6Example 4: In my school, there are 5 teachers and 170 students. The ratio of teachers to students in my school is 5 : 170. Count the number of teachers and students in your school. What is the ratio of teachers to students in your school? Write it below. ______ : ______ Is the teacher-to-student ratio in your school proportional to the one in my school?
Answer

This one needs your own school’s figures, but here is exactly how to settle it.

Given school: 5 : 170, HCF = 5 → 1 : 34
(one teacher for every 34 students)

Count the teachers and the students in your school, write the ratio, and reduce it. Then compare:

  • If your simplest form is also 1 : 34, the two ratios are proportional.
  • If it is 1 : 25, each teacher in your school handles fewer students.
  • If it is 1 : 40, each teacher handles more.
Q7Example 5: Measure the width and height (to the nearest cm) of the blackboard in your classroom. What is the ratio of width to height of the blackboard? ______ : ______ Can you draw a rectangle in your notebook whose width and height are proportional to the ratio of the blackboard?
Answer

Measure with a metre scale and reduce the ratio you get. A very common classroom size is 240 cm by 120 cm.

Width : height = 240 : 120, HCF = 120 → 2 : 1

To draw a proportional rectangle in your notebook, pick any convenient factor and multiply both terms by it:

FactorWidthHeightRatio
× 4 cm8 cm4 cm2 : 1
× 5 cm10 cm5 cm2 : 1
× 6.5 cm13 cm6.5 cm2 : 1
Q8Compare the rectangle you have drawn to those drawn by your classmates. Do they all look the same?
Answer

They will be of different sizes but the same shape — every one of them is a scaled copy of the blackboard.

In-text Questions — Pages 164–1657.4 Problem Solving with Proportional Reasoning (Examples 6–7) · Filter Coffee!

Math Talk
Q1Example 6: When Neelima was 3 years old, her mother’s age was 10 times her age. What is the ratio of Neelima’s age to her mother’s age? What would be the ratio of their ages when Neelima is 12 years old? Would it remain the same?
Answer

At age 3 the ratio is 1 : 10; at age 12 it is 4 : 13. No, it does not remain the same.

Neelima 3, mother 3 × 10 = 30 → 3 : 30 = 1 : 10
12 − 3 = 9 years later, mother is 30 + 9 = 39
12 : 39, HCF = 3 → 4 : 13
Q2Example 7: Fill in the missing numbers for the following ratios that are proportional to 14 : 21. ______ : 42 6 : ______ 2 : ______
Answer

28 : 42, 6 : 9, 2 : 3.

14 : 21 in simplest form is 2 : 3 (HCF = 7)

___ : 42 → 42 ÷ 21 = 2, so first term = 14 × 2 = 28
6 : ___ → 6 ÷ 14 = 3⁄7, so second term = 21 × 3⁄7 = 9
2 : ___ → 14 ÷ 7 = 2, so second term = 21 ÷ 7 = 3
Q3What factor should we multiply 14 by to get 6? Can it be an integer? Or should it be a fraction?
Answer

The factor is 3⁄7 — it must be a fraction, not an integer.

14y = 6
y = 6⁄14 = 3⁄7
Q4Why is this coffee stronger?
Answer

Because it has more decoction for the same amount of milk: 20 : 30 = 2 : 3, against the regular 15 : 35 = 3 : 7.

Regular: 15 mL decoction + 35 mL milk = 50 mL cup → decoction is 15⁄50 = 30%
Stronger: 20 mL decoction + 30 mL milk = 50 mL cup → decoction is 20⁄50 = 40%
Q5Why is this coffee lighter?
Answer

Because a smaller share of the cup is decoction.

Lighter: 10 mL decoction + 40 mL milk = 50 mL cup → decoction is 10⁄50 = 20%
Ratio 10 : 40 = 1 : 4, against the regular 15 : 35 = 3 : 7
Q6The following table shows the different ratios in which Manjunath mixes coffee decoction with milk. Write in the last column if the coffee is stronger or lighter than the regular coffee.
Coffee Decoction (in mL)Milk (in mL)Regular/Strong/Light
300600
150500
200400
2456
100300
The table on page 165. Manjunath’s regular filter coffee is 15 mL of coffee decoction mixed with 35 mL of milk (page 164).
Answer

Reduce each row and compare it with the regular mix, 15 : 35 = 3 : 7.

Coffee decoction (mL)Milk (mL)Simplest formDecoction in the cupRegular / Strong / Light
3006001 : 2300⁄900 = 33.3%Strong
1505003 : 10150⁄650 = 23.1%Light
2004001 : 2200⁄600 = 33.3%Strong
24563 : 724⁄80 = 30%Regular
1003001 : 3100⁄400 = 25%Light

Figure it Out — Pages 165–1677.4 Problem Solving with Proportional Reasoning

Math Talk
Q1Circle the following statements of proportion that are true.
(i) 4 : 7 :: 12 : 21
(ii) 8 : 3 :: 24 : 6
(iii) 7 : 12 :: 12 : 7
(iv) 21 : 6 :: 35 : 10
(v) 12 : 18 :: 28 : 12
(vi) 24 : 8 :: 9 : 3
Answer

True: (i), (iv) and (vi).

StatementCross multiply (ad and bc)Simplest formsTrue?
(i) 4 : 7 :: 12 : 214 × 21 = 84, 7 × 12 = 844 : 7 and 4 : 7True
(ii) 8 : 3 :: 24 : 68 × 6 = 48, 3 × 24 = 728 : 3 and 4 : 1False
(iii) 7 : 12 :: 12 : 77 × 7 = 49, 12 × 12 = 1447 : 12 and 12 : 7False
(iv) 21 : 6 :: 35 : 1021 × 10 = 210, 6 × 35 = 2107 : 2 and 7 : 2True
(v) 12 : 18 :: 28 : 1212 × 12 = 144, 18 × 28 = 5042 : 3 and 7 : 3False
(vi) 24 : 8 :: 9 : 324 × 3 = 72, 8 × 9 = 723 : 1 and 3 : 1True
Q2Give 3 ratios that are proportional to 4 : 9. ______ : ______ ______ : ______ ______ : ______
Answer

8 : 18, 12 : 27, 16 : 36 — and there are infinitely many more.

4 : 9 × 2 → 8 : 18
4 : 9 × 3 → 12 : 27
4 : 9 × 4 → 16 : 36
Q3Fill in the missing numbers for these ratios that are proportional to 18 : 24. 3 : ______ 12 : ______ 20 : ______ 27 : ______
Answer

First reduce: 18 : 24 = 3 : 4 (HCF = 6). Every answer must reduce to 3 : 4, so the second term is always 4⁄3 of the first.

3 : ___ → 3 × 4⁄3 = 4 → 3 : 4
12 : ___ → 12 × 4⁄3 = 16 → 12 : 16
20 : ___ → 20 × 4⁄3 = 80⁄3 = 26⅔ → 20 : 26⅔
27 : ___ → 27 × 4⁄3 = 36 → 27 : 36
Q4Look at the following rectangles. Which rectangles are similar to each other? You can verify this by measuring the width and height using a scale and comparing their ratios.
ABCDE
The five rectangles A to E printed on page 166; three of them are printed at a slant.
Answer

A and D are similar to each other, and C and E are similar to each other. B is not similar to any of them.

Measure each rectangle’s two sides with your scale — three of them are printed at a slant, so measure along the sides, not across the page. Rounded to the nearest millimetre:

RectangleShorter sideLonger sideLonger : shorterNearest simple ratio
A6 mm18 mm3.03 : 1
B12 mm18 mm1.53 : 2
C20 mm51 mm2.555 : 2
D13 mm39 mm3.03 : 1
E7 mm17 mm2.435 : 2
Q5Look at the following rectangle. Can you draw a smaller rectangle and a bigger rectangle with the same width to height ratio in your notebooks? Compare your rectangles with your classmates’ drawings. Are all of them the same? If they are different from yours, can you think why? Are they wrong?
The rectangle printed on page 166 (drawn here to the same shape).
Answer

The printed rectangle measures about 35 mm × 21 mm, so its width : height is 5 : 3. Multiply both terms by the same factor to get as many copies as you like.

FactorWidthHeightRatio
× 0.4 cm (smaller)2 cm1.2 cm5 : 3
the printed one3.5 cm2.1 cm5 : 3
× 1.6 cm (bigger)8 cm4.8 cm5 : 3

No, your classmates’ rectangles will not all be the same size — and no, they are not wrong.

Q6The following figure shows a small portion of a long brick wall with patterns made using coloured bricks. Each wall continues this pattern throughout the wall. What is the ratio of grey bricks to coloured bricks? Try to give the ratios in their simplest form.
(a)(b)
Page 166 — a small portion of walls (a) and (b).
Answer

(a) 9 : 6 = 3 : 2 (b) 16 : 12 = 4 : 3

Wall (a) — one repeating block = 5 columns × 3 rows = 15 bricks.

Top row: 3 coloured, 2 grey
Middle row: 2 coloured, 3 grey
Bottom row: 1 coloured, 4 grey
Coloured = 3 + 2 + 1 = 6, grey = 15 − 6 = 9
grey : coloured = 9 : 6 = 3 : 2

Wall (b) — one repeating block = 4 columns × 7 rows = 28 bricks.

Rows from the top: 1, 2, 2, 2, 2, 2, 1 coloured
Coloured = 1 + 2 + 2 + 2 + 2 + 2 + 1 = 12, grey = 28 − 12 = 16
grey : coloured = 16 : 12 = 4 : 3
Q7Let us draw some human figures. Measure your friend’s body — the lengths of their head, torso, arms, and legs. Write the ratios as mentioned below— head : torso ______ : ______ torso : arms ______ : ______ torso : legs ______ : ______ Now, draw a figure with head, torso, arms, and legs with equivalent ratios as above. Does the drawing look more realistic if the ratios are proportional? Why? Why not?
Answer

Measure with a tape and record the lengths, then reduce each pair. Here is one real set of measurements from a student about 150 cm tall:

PartLengthRatio asked forSimplest form
head22 cmhead : torso = 22 : 552 : 5
torso55 cmtorso : arms = 55 : 6011 : 12
arms60 cmtorso : legs = 55 : 8011 : 16
legs80 cm——

To draw the figure, choose one convenient factor and apply it to every measurement. Using 1⁄5 of the real lengths: head 4.4 cm, torso 11 cm, arms 12 cm, legs 16 cm.

Yes, the drawing looks far more realistic when the ratios are kept.

In-text Questions — Pages 167–170Trairasika — The Rule of Three (Examples 8–10) · Activity 1

Q1Example 8: For the mid-day meal in a school with 120 students, the cook usually makes 15 kg of rice. On a rainy day, only 80 students came to school. How many kilograms of rice should the cook make so that the food is not wasted?
Answer

10 kg of rice.

students : rice must stay proportional
120 : 15 :: 80 : ?
Factor of change = 80⁄120 = 2⁄3
Rice = 15 × 2⁄3 = 10 kg
Q2What is the factor of change in the first term?
Answer

2⁄3 — the number of students has fallen to two-thirds of what it usually is.

80⁄120 = 8⁄12 = 2⁄3

A factor smaller than 1 means the quantity has decreased. The second term must be multiplied by the very same 2⁄3.

Q3Example 9: A car travels 90 km in 150 minutes. If it continues at the same speed, what distance will it cover in 4 hours?
Answer

144 km.

4 hours = 4 × 60 = 240 minutes
150 : 90 :: 240 : x
Cross multiplying: 150 × x = 240 × 90
x = (240 × 90) ÷ 150
x = 21600 ÷ 150 = 144 km
Q4Is this the right way to formulate the question?
Answer

No. The statement 150 : 90 :: 4 : ? mixes units — 150 is in minutes but 4 is in hours.

Wrong: 150 min : 90 km :: 4 h : ?
Right: 4 h = 240 min, so 150 : 90 :: 240 : ?
Q5How can you find the distance covered in 240 minutes? Discuss with your classmates and find the answer using different strategies.
Answer

All three routes below give 144 km. Use whichever you find clearest.

  • Unitary method. In 1 minute the car covers 90 ÷ 150 = 0.6 km. In 240 minutes it covers 240 × 0.6 = 144 km.
  • Scaling the ratio. 240 ÷ 150 = 8⁄5, so multiply the distance by 8⁄5 as well: 90 × 8⁄5 = 144 km.
  • Splitting the time. 150 min → 90 km, so 300 min → 180 km and 30 min → 18 km. Then 240 = 300 − 60, and 60 min → 36 km, giving 180 − 36 = 144 km.
Q6Example 10: A small farmer in Himachal Pradesh sells each 200 g packet of tea for ₹200. A large estate in Meghalaya sells each 1 kg packet of tea for ₹800. Are the weight-to-price ratios in both places proportional?
Answer

No, they are not proportional. First put both weights in the same unit.

Himachal: 200 g : ₹200 → HCF 200 → 1 : 1
Meghalaya: 1 kg = 1000 g, so 1000 : 800 → HCF 200 → 5 : 4
1 : 1 is not 5 : 4, so the ratios are not proportional
Q7Which tea is more expensive? Why?
Answer

The Himachal tea is more expensive — ₹1,000 per kg against ₹800 per kg.

Meghalaya: 1 kg costs ₹800
Himachal: 200 g is 1⁄5 of a kg, so if 1 kg costs ₹x,
1⁄5 × x = 200
x = 200 × 5 = ₹1,000
Q8Activity 1: Take your favourite dish. Find out all the ingredients and their respective quantities needed to make the dish for your family. Suppose you are celebrating a festival and you want to invite 15 guests. Find out the quantities of the ingredients required to cook the same dish for them.
Answer

Write the family recipe first, then scale every ingredient by one factor. Here is a worked example for upma cooked for a family of 5, with 15 guests invited so that 20 people must be fed.

Factor of change = 20⁄5 = 4
IngredientFor 5 people× 4For 20 people
Rava (semolina)250 g250 × 41000 g = 1 kg
Water600 mL600 × 42400 mL = 2.4 L
Onion1 medium1 × 44 medium
Oil2 tablespoons2 × 48 tablespoons
Salt1 teaspoon1 × 44 teaspoons

Figure it Out — Pages 170–171Trairasika — The Rule of Three

Q1The Earth travels approximately 940 million kilometres around the Sun in a year. How many kilometres will it travel in a week?
Answer

About 1,80,76,923 km, that is roughly 1.81 crore kilometres in one week.

1 year ≈ 52 weeks
940 million km = 940 × 10⁶ = 94,00,00,000 km
52 : 940000000 :: 1 : x
x = 940000000 ÷ 52
x = 1,80,76,923 km (approximately)
Q2A mason is building a house in the shape shown in the diagram. He needs to construct both the outer walls and the inner wall that separates two rooms. To build a wall of 10-feet, he requires approximately 1450 bricks. How many bricks would he need to build the house? Assume all walls are of the same height and thickness.
12 ft15 ft9 ft9 ft6 ft
Page 171 — plan of the house (measurements in feet).
Answer

15,660 bricks. First add up every foot of wall in the plan, then scale.

Top block (9 ft and 15 ft rooms, both 12 ft deep):
top edge 9 + 15 = 24 ft
bottom edge 9 + 15 = 24 ft
left side 12 ft, right side 12 ft
inner dividing wall 12 ft
Lower room (6 ft × 9 ft):
left 9 ft, right 9 ft, bottom 6 ft

Total = 24 + 24 + 12 + 12 + 12 + 9 + 9 + 6 = 108 ft
10 : 1450 :: 108 : x
10 × x = 108 × 1450
x = 156600 ÷ 10 = 15,660 bricks

In-text Questions — Pages 171–172Trairasika — The Rule of Three · Activity 2

Math Talk
Q1Puneeth’s father went from Lucknow to Kanpur in 2 hours by riding his motorcycle at a speed of 50 km/h. If he drives at 75 km/h, how long will it take him to reach Kanpur? Can we form this problem as a proportion — 50 : 2 :: 75 : __ Would it take Puneeth’s father more time or less time to reach Kanpur? Think about it.
Answer

He will take less time — 1 hour 20 minutes. No, the problem cannot be written as 50 : 2 :: 75 : __, because when the speed increases, the time decreases.

Distance = speed × time = 50 × 2 = 100 km
At 75 km/h: time = 100 ÷ 75 = 4⁄3 hours
4⁄3 h = 1 h + 1⁄3 × 60 min = 1 hour 20 minutes
Q2Activity 2: Go to the market and collect the prices of different sizes of shampoo containers of the same shampoo and create a table like the one given below. See if the volume of shampoo is proportional to the price. (Sachet 6 mL ₹2; Small Bottle 180 mL ₹154; Medium Bottle 340 mL ₹276; Large Bottle 1000 mL ₹540)
Answer

Collect real prices from a shop, then work out the price of one millilitre for each size — that single number makes all four containers comparable. For the sample table in the book:

ContainerVolumePricePrice ÷ volumeCost of 1 mL
Sachet6 mL₹22 ÷ 6₹0.33
Small Bottle180 mL₹154154 ÷ 180₹0.86
Medium Bottle340 mL₹276276 ÷ 340₹0.81
Large Bottle1000 mL₹540540 ÷ 1000₹0.54

The volume is not proportional to the price. If it were, every row of the last column would show the same figure; instead it runs 0.33, 0.86, 0.81, 0.54.

Q3The ratio of the volume of a sachet to a small bottle is 6 : 180. The ratio of their prices is 2 : 154. Are these ratios proportional?
Answer

No.

Volumes: 6 : 180, HCF = 6 → 1 : 30
Prices: 2 : 154, HCF = 2 → 1 : 77
1 : 30 is not 1 : 77

Cross multiplication says the same thing: 6 × 154 = 924 while 180 × 2 = 360.

Q4Why do you think that the ratio of the prices is not proportional to the ratio of the volumes? Discuss the pros and cons of different size bottles for the company and for customers. For reducing ecological footprint, what would you recommend to the company and to the customer? Does the same occur for other products?
Answer

The price of a container is not only the price of what is inside it.

Why not proportional: every pack has fixed costs (bottle, cap, label, filling, transport) that are spread over more shampoo in a big bottle; companies also give discounts on big packs and keep sachets cheap so that everyone can afford them.

Small packsLarge packs
For the customerLow price today, easy to carry, no waste if used rarelyUsually cheaper per mL, fewer trips to the shop
For the companyReaches more buyers, but far more packaging and handling per litre soldLess packaging and handling per litre, larger sale at one go

To reduce the ecological footprint: customers should buy the largest size they will actually use up and refill it; companies should sell refill packs and take back empty bottles.

Other products: yes, many packed goods cost less per unit in bigger packs; staples like rice or atta are usually priced closer to proportion.

In-text Questions — Pages 172–1757.5 Sharing, but Not Equally! · Activity 3 · Examples 11–12

Q1Activity 3: Form a pair. Collect 12 countable objects or counters (it can be coins, seeds, or pebbles). Now, share them between the two of you in different ways. If you divide them equally, what is the ratio of the number of counters with each of you?
Answer

6 : 6, which in its simplest form is 1 : 1.

12 ÷ 2 = 6 counters each
6 : 6, HCF = 6 → 1 : 1
Q2If your partner gets 5 counters, how many objects will you get? What is the ratio of the counters?
Answer

You get 7 counters, and the ratio of your partner’s counters to yours is 5 : 7.

12 − 5 = 7
partner : you = 5 : 7, and 5 and 7 have HCF 1, so it is already simplest
Q3Now, if you want to share the counters between the two of you in the ratio of 3 : 1, how many counters would each of you get?
Answer

Your partner gets 9, you get 3.

Deal the counters out 3 and 1 at a time and see where it lands:

RoundPartner takesYou takeCounters left
start——12
1318
2314
3310
total93—
Or in one step: 3 + 1 = 4 groups, each group is 12 ÷ 4 = 3 counters
Partner: 3 × 3 = 9 You: 1 × 3 = 3
Check: 9 : 3 = 3 : 1 ✓ and 9 + 3 = 12 ✓
Q4Now, if you want to share 42 counters between the two of you in the ratio of 4 : 3, how will you do it?
Answer

Your partner gets 24, you get 18.

Total groups = 4 + 3 = 7
Size of each group = 42 ÷ 7 = 6
Partner: 4 × 6 = 24 You: 3 × 6 = 18
Check: 24 + 18 = 42 ✓ and 24 : 18 = 4 : 3 ✓
Q5What is the size of each group?
Answer

6 counters.

Number of groups = 4 + 3 = 7
Size of each group = 42 ÷ 7 = 6

Every one of the seven groups holds 6 counters; four of them go to your partner and three to you.

Q6Example 11: Prashanti and Bhuvan started a food cart business near their school. Prashanti invested ₹75,000 and Bhuvan invested ₹25,000. At the end of the first month, they gained a profit of ₹4,000. They decided that they would share the profit in the same ratio as that of their investment. What is each person’s share of the profit?
Answer

Prashanti gets ₹3,000 and Bhuvan gets ₹1,000.

Ratio of investments = 75000 : 25000 = 3 : 1 (HCF = 25000)
Total groups = 3 + 1 = 4
Each group = 4000 ÷ 4 = ₹1,000
Prashanti = 3 × 1000 = ₹3,000
Bhuvan = 1 × 1000 = ₹1,000
Check: 3000 + 1000 = 4000 ✓ and 3000 : 1000 = 3 : 1 ✓
Q7Example 12: A mixture of 40 kg contains sand and cement in the ratio of 3 : 1. How much cement should be added to the mixture to make the ratio of sand to cement 5 : 2?
Answer

2 kg of cement should be added.

Sand = 3⁄(3 + 1) × 40 = 30 kg; cement = 1⁄(3 + 1) × 40 = 10 kg
Sand stays 30 kg. New ratio: 5 : 2 :: 30 : ?
Cement needed = 2⁄5 × 30 = 12 kg
Cement to add = 12 − 10 = 2 kg

Figure it Out — Page 1757.5 Sharing, but Not Equally!

Q1Divide ₹4,500 into two parts in the ratio 2 : 3.
Answer

₹1,800 and ₹2,700.

Total groups = 2 + 3 = 5
Each group = 4500 ÷ 5 = ₹900
First part = 2 × 900 = ₹1,800
Second part = 3 × 900 = ₹2,700
Check: 1800 + 2700 = 4500 ✓ and 1800 : 2700 = 2 : 3 ✓
Q2In a science lab, acid and water are mixed in the ratio of 1 : 5 to make a solution. In a bottle that has 240 mL of the solution, how much acid and water does the solution contain?
Answer

40 mL of acid and 200 mL of water.

Total groups = 1 + 5 = 6
Each group = 240 ÷ 6 = 40 mL
Acid = 1 × 40 = 40 mL
Water = 5 × 40 = 200 mL
Check: 40 + 200 = 240 ✓ and 40 : 200 = 1 : 5 ✓
Q3Blue and yellow paints are mixed in the ratio of 3 : 5 to produce green paint. To produce 40 mL of green paint, how much of these two colours are needed? To make the paint a lighter shade of green, I added 20 mL of yellow to the mixture. What is the new ratio of blue and yellow in the paint?
Answer

15 mL of blue and 25 mL of yellow. After adding the yellow, the new ratio is 1 : 3.

Total groups = 3 + 5 = 8
Each group = 40 ÷ 8 = 5 mL
Blue = 3 × 5 = 15 mL Yellow = 5 × 5 = 25 mL

Add 20 mL of yellow: yellow = 25 + 20 = 45 mL, blue is still 15 mL
blue : yellow = 15 : 45, HCF = 15 → 1 : 3
Q4To make soft idlis, you need to mix rice and urad dal in the ratio of 2 : 1. If you need 6 cups of this mixture to make idlis tomorrow morning, how many cups of rice and urad dal will you need?
Answer

4 cups of rice and 2 cups of urad dal.

Total groups = 2 + 1 = 3
Each group = 6 ÷ 3 = 2 cups
Rice = 2 × 2 = 4 cups
Urad dal = 1 × 2 = 2 cups
Check: 4 + 2 = 6 ✓ and 4 : 2 = 2 : 1 ✓
Q5I have one bucket of orange paint that I made by mixing red and yellow paints in the ratio of 3 : 5. I added another bucket of yellow paint to this mixture. What is the ratio of red paint to yellow paint in the new mixture?
Answer

3 : 13.

In one bucket of orange paint:
red = 3⁄8 bucket, yellow = 5⁄8 bucket
Add 1 whole bucket of yellow:
yellow = 5⁄8 + 1 = 13⁄8 bucket, red is unchanged at 3⁄8
red : yellow = 3⁄8 : 13⁄8
Multiply both terms by 8 → 3 : 13

Figure it Out — Pages 176–1777.6 Unit Conversions (chapter-end set)

Try This
Q1Anagh mixes 600 mL of orange juice with 900 mL of apple juice to make a fruit drink. Write the ratio of orange juice to apple juice in its simplest form.
Answer

2 : 3.

orange : apple = 600 : 900
HCF of 600 and 900 = 300
600⁄300 : 900⁄300 = 2 : 3
Q2Last year, we hired 3 buses for the school trip. We had a total of 162 students and teachers who went on that trip and all the buses were full. This year we have 204 students. How many buses will we need? Will all the buses be full?
Answer

4 buses are needed, and they will not all be full — 12 seats will be empty.

Seats in one bus = 162 ÷ 3 = 54
Buses needed = 204 ÷ 54 = 3.78, so 4 buses
Seats in 4 buses = 4 × 54 = 216
Empty seats = 216 − 204 = 12
Q3The area of Delhi is 1,484 sq. km and the area of Mumbai is 550 sq. km. The population of Delhi is approximately 30 million and that of Mumbai is 20 million people. Which city is more crowded? Why do you say so?
Answer

Mumbai is more crowded — about 36,364 people in every square kilometre, against about 20,216 in Delhi.

Delhi: 30 million ÷ 1484 = 3,00,00,000 ÷ 1484 ≈ 20,216 people per sq km
Mumbai: 20 million ÷ 550 = 2,00,00,000 ÷ 550 ≈ 36,364 people per sq km
Q4A crane of height 155 cm has its neck and the rest of its body in the ratio 4 : 6. For your height, if your neck and the rest of the body also had this ratio, how tall would your neck be?
Answer

Your neck would be 4⁄10 = 2⁄5 of your height. Measure yourself and multiply.

Total groups = 4 + 6 = 10
Neck = 4⁄10 × your height = 0.4 × your height

For the crane: 4⁄10 × 155 = 62 cm of neck
If you are 150 cm tall: 4⁄10 × 150 = 60 cm
If you are 160 cm tall: 4⁄10 × 160 = 64 cm
Q5Let us try an ancient problem from Lilavati. At that time weights were measured in a unit named palas and niskas was a unit of money. “If 2½ palas of saffron costs 3⁄7 niskas, O expert businessman! tell me quickly what quantity of saffron can be bought for 9 niskas?”
Answer

52.5 palas of saffron.

2½ palas = 5⁄2 palas, cost = 3⁄7 niskas
3⁄7 : 5⁄2 :: 9 : x
Cross multiplying: 3⁄7 × x = 5⁄2 × 9
3⁄7 × x = 45⁄2
x = 45⁄2 × 7⁄3 = 315⁄6 = 52.5 palas
Q6Harmain is a 1-year-old girl. Her elder brother is 5 years old. What will be Harmain’s age when the ratio of her age to her brother’s age is 1 : 2?
Answer

Harmain will be 4 years old (and her brother 8), that is, after 3 years.

Let the number of years from now be x.
Harmain: 1 + x, brother: 5 + x
(1 + x) : (5 + x) = 1 : 2
Cross multiplying: 2(1 + x) = 1(5 + x)
2 + 2x = 5 + x
x = 3
Harmain’s age = 1 + 3 = 4 years, brother = 5 + 3 = 8 ✓ and 4 : 8 = 1 : 2 ✓
Q7The mass of equal volumes of gold and water are in the ratio 37 : 2. If 1 litre of water is 1 kg in mass, what is the mass of 1 litre of gold?
Answer

18.5 kg.

gold : water = 37 : 2 for equal volumes
37 : 2 :: x : 1
2 × x = 37 × 1
x = 37⁄2 = 18.5 kg
Q8It is good farming practice to apply 10 tonnes of cow manure for 1 acre of land. A farmer is planning to grow tomatoes in a plot of size 200 ft by 500 ft. How much manure should he buy? (Please refer to the section on Unit Conversions earlier in this chapter).
Answer

About 22.96 tonnes, that is roughly 22,957 kg of cow manure.

Area of plot = 200 × 500 = 1,00,000 sq ft
1 acre = 43,560 sq ft
Plot in acres = 100000 ÷ 43560 = 2.2957 acres
Manure = 10 × 2.2957 = 22.957 tonnes ≈ 22.96 tonnes
In kilograms: 22.957 × 1000 ≈ 22,957 kg
Q9A tap takes 15 seconds to fill a mug of water. The volume of the mug is 500 mL. How much time does the same tap take to fill a bucket of water if the bucket has a 10-litre capacity?
Answer

300 seconds, that is 5 minutes.

10 litres = 10 × 1000 = 10,000 mL
Number of mugfuls = 10000 ÷ 500 = 20
Time = 20 × 15 = 300 seconds = 5 minutes
Q10One acre of land costs ₹15,00,000. What is the cost of 2,400 square feet of the same land?
Answer

About ₹82,645.

1 acre = 43,560 sq ft costs ₹15,00,000
43560 : 1500000 :: 2400 : x
43560 × x = 2400 × 15,00,000
x = 3,60,00,00,000 ÷ 43560
x = ₹82,644.63 ≈ ₹82,645
Q11A tractor can plough the same area of a field 4 times faster than a pair of oxen. A farmer wants to plough his 20-acre field. A pair of oxen takes 6 hours to plough an acre of land. How much time would it take if the farmer used a pair of oxen to plough the field? How much time would it take him if he decides to use a tractor instead?
Answer

Oxen: 120 hours. Tractor: 30 hours.

Oxen: 6 hours for 1 acre
1 : 6 :: 20 : t ⇒ t = 20 × 6 = 120 hours

The tractor is 4 times faster, so it needs one-fourth of the time:
Per acre: 6 ÷ 4 = 1.5 hours
For 20 acres: 20 × 1.5 = 30 hours, or simply 120 ÷ 4 = 30 hours
Q12The ₹10 coin is an alloy of copper and nickel called ‘cupro-nickel’. Copper and nickel are mixed in a 3 : 1 ratio to get this alloy. The mass of the coin is 7.74 grams. If the cost of copper is ₹906 per kg and the cost of nickel is ₹1,341 per kg, what is the cost of these metals in a ₹10 coin?
Answer

Copper ≈ ₹5.26, nickel ≈ ₹2.59, together about ₹7.85.

Total groups = 3 + 1 = 4, each group = 7.74 ÷ 4 = 1.935 g
Copper = 3 × 1.935 = 5.805 g
Nickel = 1 × 1.935 = 1.935 g

Copper: ₹906 per 1000 g → 5.805 × 906 ÷ 1000 = 5259.33 ÷ 1000 = ₹5.26
Nickel: ₹1341 per 1000 g → 1.935 × 1341 ÷ 1000 = 2594.835 ÷ 1000 = ₹2.59
Total metal cost ≈ ₹7.85

Puzzle Time — BinairoBinairo (Takuzu) — end of Part I

Try This
Q1Solve the following Binairo puzzles: (first grid)
The first 6 × 6 Binairo puzzle on page 178. Red bars are vertical lines, dark bars are horizontal lines; the other cells are empty.
Answer

Here is the completed grid. Shaded cells are the ones printed in the book.

Puzzle 1 solved. The shaded cells are the ones the book gives; every row and every column has three vertical and three horizontal lines, no three alike are adjacent, and all six rows and all six columns are different.
Q2Solve the following Binairo puzzles: (second grid)
The second 6 × 6 Binairo puzzle on page 178. Red bars are vertical lines, dark bars are horizontal lines; the other cells are empty.
Answer

The completed grid:

Puzzle 2 solved. The shaded cells are the ones the book gives; every row and every column has three vertical and three horizontal lines, no three alike are adjacent, and all six rows and all six columns are different.
Q3Solve the following Binairo puzzles: (third grid)
The third 6 × 6 Binairo puzzle on page 178. Red bars are vertical lines, dark bars are horizontal lines; the other cells are empty.
Answer

The completed grid:

Puzzle 3 solved. The shaded cells are the ones the book gives; every row and every column has three vertical and three horizontal lines, no three alike are adjacent, and all six rows and all six columns are different.

Chapter 7 of 13 – Maths

Also for This Chapter

NCERT Solutions Class 8 Maths Chapter 7 Proportional Reasoning 1 – Overview

ClassClass 8
SubjectMaths
Chapter7 – Proportional Reasoning 1
Textbook pages159 – 177
Questions solved69
Session2027
FormatFull answers on this page + PDF

NCERT Solutions Class 8 Maths Chapter 7 – FAQs

Where can I download NCERT Solutions Class 8 Maths Chapter 7 Proportional Reasoning 1 PDF?

Read every answer on this page, or download the free PDF from the table at the top.

Is this for the 2027 session?

Yes, it follows the latest NCERT Class 8 Maths book for 2027.

How many questions are solved in NCERT Class 8 Maths Chapter 7?

All 69 questions of the chapter (textbook pages 159 – 177) – the in-text questions, activities and the end-of-chapter exercises.

How should I use these solutions?

Read the chapter in the NCERT book first, attempt the questions yourself, then check your answers here.

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