Page 173 - Start Up Mathematics_8 (Non CCE)

100
If Karishma’s income is ` 100, Pooja’s income = ` × 100 = ` 125
80
\ Pooja’s income is (125 – 100)% or 25% more than Karishma’s income.
Example 8: A mixture of milk and water contains 8 parts of milk and 2 parts of water. What is the
percentage of milk and water in the mixture?
Solution: Ratio of milk and water in the mixture = 8 : 2
\ sum of ratios = 8 + 2 = 10
In 10 parts of mixture, milk is 8 parts
8
In 1 part of mixture, milk is parts
10
8
\ in 100 parts of mixture, milk is ¥ 100 = 80%
10
Again, in 10 parts of mixture, water is 2 parts
2
In 1 part of mixture, water is parts
10
2
In 100 parts of mixture, water is × 100 = 20%
10
\ percentage of milk in mixture = 80%

and percentage of water in mixture = 20%
Example 9: The value of a washing machine depreciates every year by 12%. What will be its value after
2 years, if its present value is ` 60,000?
Solution: Present value of washing machine = ` 60,000
12
Decrease in value after 1 year = 12% of 60,000 = ` Ê 100 ¥ 60 000, ˆ = ` 7,200
Á
˜
Ë
¯
\ Depreciated value after 1 year = ` (60,000 – 7,200) = ` 52,800
12
Decrease in value after 2 years = 12% of 52,800 = ` Ê Á Ë 100 ¥ 52 800, ˆ ˜ ¯ = ` 6,336

\ Depreciated value after 2 years = ` (52,800 – 6,336) = ` 46,464

Hence, the value of washing machine after 2 years = ` 46,464
Example 10: The population of a city increases 20% annually. If the present population is 24,600; find the
population a year ago.
Solution: Present population = 24,600 ...(1)
Let the population of the city a year ago be x.
20 x
Increase in population = 20% of x = x =
100 5
x 6 x
\ Present population = x + = ...(2)
6x 5 5
From (1) and (2), = 24,600
5
fi 6x = 24,600 × 5

24 600 5, ¥
fi x = = 20 500,
6
\ population of the city a year ago = 20,500
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