NCERT Solutions for Class 8 Maths Chapter 7 Comparing Quantities Ex 7.1
Ex 7.1 Class 8 Maths Question 1.
Find the ratio of the following.
(a) Speed of a cycle is 15 km per hour to the speed of scooter 30 km per hour.
(b) 5 m to 10 km
(c) 50 paise to ₹ 5
Solution:
(a) Ratio of the speed of the cycle to the speed of the scooter = 15 km : 30 km = 1 : 2.
(b) Ratio of 5 m to 10 km = 5 m : 10 km [∵ 1 km = 1000 m, ∴ 10 km = 10000 m]
= 5 m : 10000 m
= 1 : 2000
[Dividing both the terms by their HCF = 5]
(c) Ratio of 50 paise to ₹ 5 = 50 paise : ₹ 5 [₹ 1 = 100 paise, ₹ 5 = 500 paise]
= 50 paise : 500 paise
= 1 : 10
[Dividing both the terms by their HCF = 50]
Ex 7.1 Class 8 Maths Question 2.
Convert the following ratios to percentages.
(a) 3 : 4
(b) 2 : 3
Solution:
Ex 7.1 Class 8 Maths Question 3.
72% of 25 students are interested in mathematics. How many are not interested in mathematics?
Solution:
The number of students who are interested in mathematics = 72% of 25
The number of students who are not interested in mathematics = 25 – 18 = 7
Ex 7.1 Class 8 Maths Question 4.
A football team won 10 matches out of the total number of matches they played. If their win percentage was 40, then how many matches did they play in all?
Solution:
Since the team won 40 matches out of 100 matches.
Therefore, the team won 1 match out of 100/40 matches.
Therefore, the team won 10 matches out of 100/40 × 10 = 25 matches
Hence, the total number of matches played by the team is 25.
Ex 7.1 Class 8 Maths Question 5.
If Chameli had ₹ 600 left after spending 75% of her money, how much did she have in the beginning?
Solution:
Let the money with Chameli be ₹ 100.
Money spent by her = 75% of 100 = 75/100 × 100 = ₹ 75
The money left with her = ₹ 100 – ₹ 75 = ₹ 25
Since ₹ 25 is left with her out of ₹ 100.
Therefore, ₹ 1 is left with her out of ₹ 100/25.
Therefore, ₹ 600 will be left out of ₹ 100/25 × 600 = ₹ 2400
Hence, Chameli had ₹ 2400 in the beginning.
Ex 7.1 Class 8 Maths Question 6.
If 60% people in a city like cricket, 30% like football and the remaining like other games, then what per cent of the people like other games? If the total number of people is 50 lakhs, find the exact number who like each type of game.
Solution:
The total number of people = 50,00,000
The number of people who like cricket = 60% of 50,00,000
= 60/100 × 50,00,000
= 30,00,000
The number of people who like football = 30% of 50,00,000
= 30/100 × 50,00,000
= 15,00,000
The number of people who like other games = 50,00,000 – (30,00,000 + 15,00,000)
= 50,00,000 – 45,00,000
= 5,00,000
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