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
