# NCERT Solutions for Class 7 Maths Chapter 8

## Comparing Quantities Class 7

### Exercise 8.1 : Solutions of Questions on Page Number : 157

Q1 :

Find the ratio of:

(a) Rs 5 to 50 paise (b) 15 kg to 210 g

(c) 9 m to 27 cm (d) 30 days to 36 hours

(a) Rs 5 to 50 paise

1 rupee = 100 paise

5 rupee = 500 paise

Hence, the required ratio is 10:1.

(b) 15 kg to 210 g

1 kg = 1000 g

15 kg = 15000 g

Hence, the required ratio is 500:7.

(c) 9 m to 27 cm

1 m = 100 cm

9 m = 900 cm

Hence, the required ratio is 100:3.

(d) 30 days to 36 hours

1 days = 24 hrs

30 days = 24 × 30 = 720 hrs

Hence, the required ratio is 20:1.

Q2 :

In a computer lab, there are 3 computers for every 6 students. How many computers will be needed for 24 students?

For 6 students, number of computers required = 3

∴ For 1 student, number of computers required =

∴ For 24 students, number of computers required == 12
Hence, 12 computers are required for 24 students.

Q3 :

Population of Rajasthan = 570 lakhs and population of UP = 1660 lakhs.

Area of Rajasthan = 3 lakh km2 and area of UP = 2 lakh km2.

(i) How many people are there per km2 in both these States?

(ii) Which State is less populated?

### Exercise 8.2 : Solutions of Questions on Page Number : 164

Q1 :

Convert the given fractional numbers to per cents.

(a) (b)

(c) (d)

Q2 :

Convert the given decimal fractions to per cents.

(a) 0.65 (b) 2.1 (c) 0.02 (d) 12.35

Q3 :

Estimate what part of the figures is coloured and hence find the per cent which is coloured.

Q4 :

Find:

(a) 15% of 250 (b) 1% of 1 hour

(c) 20% of Rs 2500 (d) 75% of 1 kg

Q5 :

Find the whole quantity if

(a) 5% of it is 600 (b) 12% of it is 1080

(c) 40% of it is 500 km (d) 70% of it is 14 minutes

(e) 8% of it is 40 litres

Q6 :

Convert given percents to decimal fractions and also to fractions in simplest forms:

(a) 25% (b) 150%

(c) 20% (d) 5%

Q7 :

In a city, 30% are females, 40% are males and remaining are children. What per cent are children?

Q8 :

Out of 15, 000 voters in a constituency, 60% voted. Find the percentage of voters who did not vote. Can you now find how many actually did not vote?

Q9 :

Meeta saves Rs 400 from her salary. If this is 10% of her salary. What is her salary?

Q10 :

A local cricket team played 20 matches in one season. It won 25% of them. How many matches did they win?

### Exercise 8.3 : Solutions of Questions on Page Number : 171

Q1 :

Tell what is the profit or loss in the following transactions. Also find profit

percent or loss percent in each case.

(a) Gardening shears bought for Rs 250 and sold for Rs 325.

(b) A refrigerator bought for Rs 12,000 and sold at Rs 13,500.

(c) A cupboard bought for Rs 2,500 and sold at Rs 3,000.

(d) A skirt bought for Rs 250 and sold at Rs 150.

Q2 :

Convert each part of the ratio to percentage:

(a) 3:1 (b) 2:3:5 (c) 1:4 (d) 1:2:5

Q3 :

The population of a city decreased from 25,000 to 24,500. Find the percentage decrease.

Q4 :

Arun bought a car for Rs 3,50,000. The next year, the price went upto

Rs 3,70,000. What was the percentage of price increase?

Q5 :

I buy a T.V. for Rs 10,000 and sell it at a profit of 20%. How much money do I get for it?

Q6 :

Juhi sells a washing machine for Rs 13, 500. She loses 20% in the bargain. What was the price at which she bought it?

Q7 :

(i) Chalk contains calcium, carbon and oxygen in the ratio 10:3:12. Find the percentage of carbon in chalk.

(ii) If in a stick of chalk, carbon is 3g, what is the weight of the chalk stick?

Q8 :

Amina buys a book for Rs 275 and sells it at a loss of 15%. How much does she sell it for?

Q9 :

Find the amount to be paid at the end of 3 years in each case:

(a) Principal = Rs 1,200 at 12% p.a.

(b) Principal = Rs 7,500 at 5% p.a.

Q10 :

What rate gives Rs 280 as interest on a sum of Rs 56,000 in 2 years?

Q11 :

If Meena gives an interest of Rs 45 for one year at 9% rate p.a.. What is the sum she has borrowed?