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1. The ratio of the number of boys and girls in a college is 7 : 8. If the percentage increase in the number of boys and girls be 20% and 10% respectively, what will be the new ratio?

A. 8 : 9

B. 17 : 18

C. 21 : 22

D. Cannot be determined

Solution:

Originally, let the number of boys and girls in the college be 7x and 8x respectively
Their increased number is (120% of 7x) and (110% of 8x)

\begin{aligned} \Rightarrow (\frac{120}{100} \times 7 x) and (\frac{110}{100} \times 8 x) \\ \Rightarrow \frac{42 x}{5} and \frac{44 x}{5} \\ ∴ The required ration \\ = \frac{42 x}{5} : \frac{44 x}{5} \\ = 21 : 22 \end{aligned}

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