## ML Aggarwal Class 7 Solutions for ICSE Maths Chapter 7 Percentage and Its applications Ex 7.2

Question 1.

Find:

(i) 15% of 250

(ii) 25% of 120 litres

(iii) 1% of 1 hour

(iv) 75% of 1 kg

(v) 120% of ₹ 250

(vi) 0.6% of 2 km

Solution:

Question 2.

8% of children of a class of 25 like getting wet in the rain. How many children like getting wet in the rain?

Solution:

Number of students in a class = 25

Number of children like getting wet in the rain = 8% of 25

= \(\frac { 8 }{ 100 }\) × 25 = 2

Question 3.

Vasundhara ate 3 ice cream cups out of 20 kept in the fridge. What per cent did she eat?

Solution:

Vasundra ate 3 icecream out of 20

Percentage = \(\frac { 8 }{ 100 }\) × 100 = 15%

Question 4.

Express:

(i) 20 as a percentage of 50

(ii) 60 litres as a percentage of 40 litres

(iii) 90 cm as a percentage of 4.5 m

(iv) 350 g as a percentage of 5.6 kg

Solution:

(i) 20 as a percentage of 50

Percentage = \(\frac { 20 }{ 50 }\) × 100 = 40%

(ii) 60 litres as a percentage of 40 litres

Percentage = \(\frac { 60 }{ 40 }\) × 100 = 150%

(iii) 90 cm as a percentage of 4.5 m

4.5 m = 450 cm

Percentage = \(\frac { 90}{ 450 }\) × 100 = 20%

(iv) 350 g as a percentage of 5.6 kg

5.6 kg = 5.6 × 1000 gm

Question 5.

What per cent is:

(i) 12 of 80

(ii) 25 paise of 4 rupees

(iii) 300 g of 2 kg

Solution:

(i) 12 of 80

Question 6.

A school team won 6 games this year against 4 games won last year. What is the per cent increase?

Solution:

A school team won 6 games this year against 4 games won last year.

Number of game more won this year = 6 – 4 = 2

Percentage = \(\frac { 2 }{ 4 }\) × 100 = 50%

Question 7.

The price of a shirt decreased from ₹ 80 to ₹ 60, find the percentage of decrease in the price of the shirt.

Solution:

Price of a shirt decreased from ₹ 80 to ₹ 60

Total decrease = ₹ 80 – ₹ 60 = ₹ 20

Percentage decreased = \(\frac { 20 }{ 80 }\) × 100 = 25%

Question 8.

My mother says, in her childhood petrol was ₹ 1 per litre. It is ₹ 65 per litre today. By what percentage has the prices of petrol gone up?

Solution:

Some years past, rate of petrol = ₹ 1 per litre

Present rate = ₹ 65 per litre

Increase = \(\frac { 65 }{ 1 }\) × 100 = 6500%

Question 9.

Rate of basmati rice last year was ₹ 40 a kg. This year they are costly by 20%. What is the price this year?

Solution:

Last year, rate of basmati = ₹ 40 per kg

Increase this year = 20%

Question 10.

300 students took an exam. 28% failed. Calculate the number of students who passed the exam.

Solution:

Total number of students = 300

Failed = 28%

Total failed = 28% of 300

= \(\frac { 28 }{ 100 }\) × 300 = 84

Number of students passed = 300 – 84 = 216

Question 11.

Out of 15000 voters in a constituency, 60% voted. Find the number of voters who did not vote.

Solution:

Total number of voters = 15000

Number of voters who cast their votes

= 15000 × \(\frac { 60 }{ 100 }\) = 9000

Number of voters who did not vote = 15000 – 9000 = 6000

Question 12.

20% of the length of a flagpole is painted green, 45% is painted yellow and the remaining red. If the length of the pole is 18 m, what length of it is painted red?

Solution:

Length of pole = 18 m

Percentage of pole which is painted green = 20%

Percerftage of pole which is painted yellow = 45%

and remaining pole = 100- (20 + 45) = 35%

and it is painted red

Length of pole which is painted red

= 35% of 18 m = \(\frac { 35 }{ 100 }\) × 18

= \(\frac { 63 }{ 10 }\)

= 6.3 m

Question 13.

Chalk contains 10% calcium, 3% carbon, 12% oxygen and the remaining sand. Find the amount of carbon and calcium (in grams) in 2\(\frac { 1 }{ 2 }\) kg of chalk. Also, find the amount of sand (in kg).

Solution:

In chalk,

Calcium = 10%

Carbon = 3%

Oxygen = 12%

Remaining = 100 – (10 + 3 + 12) = 100 – 25 = 75%

Sand = 75%

Question 14.

Find the whole quantity if:

(i) 25% of it is 9

(ii) 75% of it is 15

(iii) 12% of it is ₹ 1080

(iv) 8% of it is 40 litres

Solution:

Question 15.

Mohini saves ₹ 400 from her salary. If this is 10% of her salary, then what is her salary?

Solution:

Mohini’s savings from her salary = ₹ 400

Which is 10% of her salary

Her salary = ₹ \(\frac { 400\times 100 }{ 10 }\)

= ₹ 4000

Question 16.

16% of the apples in a basket go bad. If there are 42 good apples in the basket, find the total number of apples in the basket.

Solution:

Good apples in the basket = 42

16% of apples in a basket go bad

Remaining good apples = 100 – 16 = 84%

Total apples in the basket = \(\frac { 42\times 100 }{ 84 }\)

= 50 apples

Question 17.

In an examination, a student has to secure 45% marks to pass the exam. If Varun got 251 marks and failed by 19 marks, what are the maximum marks?

Solution:

Pass marks in an examination = 45%

Varun got 251 marks but fails by 19 marks

Pass marks = 251 + 19 = 270

45% of total marks = 270

Total marks = \(\frac { 270\times 100 }{ 45 }\)

= 600 marks

Question 18.

On a rainy day, 94% of the students were students absent on that day was 174, find the total strength of the school.

Solution:

On a rainy day,

Number of students who were present = 94%

Number of students who were absent = 174

Percentage of absent students = 100 – 94 = 6%

6% of total students = 174

= \(\frac { 174\times 100 }{ 6 }\)

= 2900 students

Question 19.

40% of the population of a town are men and 39% are women. If the number of children is 12600, find the number of men.

Sol.

Let the whole population be x

Number of men = 40% of x = \(\frac { 40x }{ 100 }\)

Number of women = 39% of x = \(\frac { 39x }{ 100 }\)

Number of children = 12600

According to given condition,

Total population = 60000

Number of men = \(\frac { 40x }{ 100 }\)

= \(\frac { 40 }{ 100 }\) × 60000

= 24000 men

Question 20.

If the price of a watch is increased by 15%, the increase in the price is ₹ 90. What was the price of watching earlier?

Solution:

Let the price of watch earlier be x.

Question 21.

(i) Find the number which when increased by 30% becomes 39.

(ii) Find the number which when decreased by 8% becomes 506.

Solution:

Let the number be x

According to statement,

x + 30% of x = 39

x + \(\frac { 30 }{ 100 }\) x = 39

Question 22.

The price of a shirt is reduced by 7% to ₹ 465. What is its original price?

Solution:

Let the original price of the shirt be x.

Rate of reduction = 7%

Reduction = 7% of x