Subject: General Aptitude · Chapter: Ratio and Proportion · Exam: 2009 · Marks: · Difficulty:
The boys and girls in a college are in the ratio 3 : 2. If 20\% of the boys and 25\% of the girls are adults, the percentage of students who are not adults is
(a)67.5\%
(b)58\%
(c)78\%
(d)82.5\%
Answer
Answer (as printed): C
Explanation
Let the number of boys and girls be $3x$ and $2x$ respectively. Then, number of boys and girls who are adults $= 20\%$ of $3x + 25\%$ of $2x = \left(\frac{20}{100} \times 3x\right) + \left(\frac{25}{100} \times 2x\right) = \frac{3x}{5} + \frac{x}{2} = \frac{11x}{10}$. $\therefore$ Number of boys and girls who are not adults $= (3x + 2x) - \frac{11x}{10} = 5x - \frac{11x}{10} = \frac{39x}{10}$. Required percentage $= \left(\frac{39x}{10} \times \frac{1}{5x} \times 100\right)\% = 78\%$.
Explanation as extracted from the printed page; notation may be imperfect.