Question 19
SSC-CGL 2020 Mar 3 Shift 1
In a class of 640 the ratio of boys to girls is 5 : 3. If the number of girls is increased by 30, how should the strength of boys be changed so that the new ratio is 14 : 9?
Solution in Brief
Boys = $\displaystyle \frac {5}{5 + 3} \times 640 = 400$
Girls = $\displaystyle 640 - 400 = 240$
New total girls $\displaystyle = 240 + 30 = 270$
new ratio $\displaystyle \frac{\text{New total boys}}{\text{New total girls}} = \frac{14}{9}$
$\displaystyle \therefore$ new total boys = $\displaystyle \frac{14}{9} \times 270 = 420$
$\displaystyle \therefore $ increase $\displaystyle 420 - 400 = 20\:\underline{Ans}$
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