Question

(a) a number is first increased by 20% and then decreased by15%. find the net increase or decrease percent.

Answer 1

Let x be the number...
Increase in the number = 20x/100 + x
$Let x be the number... \\ Increase in the number = \frac{20x}{100} + x \\ decrease \: in \: the \: number \: = \\ \frac{20x}{100} - \frac{15 \times \frac{20x}{100} }{100} \\ = \frac{17x}{100} \\ therefore \: the \: net \: increaese \: in \: \\ the \: amount \: is \: = \frac{17}{100} \\ \: \: \: = 17\%$
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Answer 2

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• Let the Number be 100.

➟ 100 × (100 + 20)% × (100 - 15)%

➟ 100 × 120% × 85%

➟ 100 × $\large\tt{\frac{120}{100}}$ × $\large\tt{\frac{85}{100}}$

➟ 100 × $\large\tt{\frac{12}{10}}$× $\large\tt{\frac{17}{20}}$

➟ 10 × 12 × $\large\tt{\frac{17}{20}}$

➟ 102%

2% increase