Page 171 - Start Up Mathematics_8 (Non CCE)

Increase/Decrease in Percent

Ê Increase ˆ Ê Decrease ˆ
Increase% = Á Original value ¥ 100 % Decrease% = Á Ë Original value ¥ 100 %
˜
˜
Ë
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Example 1: Find 15% of ` 1,500.
15
Solution: 15% of ` 1,500 = ` ¥ 1 500, = ` 225
100
Example 2: What percent is 10 of 50?
Solution: Let 10 be x% of 50.

x
fi x% of 50 = 10 fi × 50 = 10
100
10 100¥
fi x × 50 = 10 × 100 fi x = 50 = 20
\ 10 is 20% of 50.
Example 3: Pratap paid 20% of his salary as income tax. If he is left with ` 8,400 after paying the tax,
find his salary.
Solution: Let Pratap’s salary be ` x.
20 x
Amount paid as income tax = 20% of x = ` × x = `
100 5
Money left after paying income tax = ` 8,400

x 5xx-
fi x – = 8,400 fi = 8,400
5 5
4x 8 400, ¥ 5
fi = 8,400 fi x = = ` 10,500
5 4
Hence, Pratap’s salary is ` 10,500.
Example 4: A medicine contains 6% benzoic acid, 36% salicylic acid and the rest methanol. Find the
volume of each in 500 mL medicine.
Solution: Total quantity of medicine = 500 mL
Ê 6 ˆ
Amount of benzoic acid = 6% of 500 mL = Á Ë 100 ¥ 500 mL = 30 mL
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¯
Ê 36 ˆ
Amount of salicylic acid = 36% of 500 mL = Á 100 ¥ 500 ˜ mL = 180 mL
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Ë
\ amount of methanol = {500 – (30 + 180)} mL = (500 – 210) mL = 290 mL
Example 5: Out of her total income, Poonam spends 25% on house rent and 60% of the rest on household
expenses. If she saves ` 2,100, what is her total income?
Solution: Let Poonam’s total income be ` 100.

Money spent on house rent = 25% of 100 = ` 25
Balance = ` (100 – 25) = ` 75
60
ˆ
Money spent on household = 60% of ` 75 = ` Ê Á Ë 100 ¥ 75 = ` 45
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\ saving = ` (75 – 45) = ` 30
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