Question

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. $58\%$
• B. $67.5\%$
• C. $78\%$
• D. $82.5\%$

Answer 1

The correct option is C $78\%$

Lets say there are $100$ students in the class

The boys and girls are in the ratio $3:2=3x:2x$ with unknown multiplier of ${}^{\prime }{x}^{\prime }$

Total number of student is $3x+2x=100$

so $5x=100$

$x=20$

Number of boys in the class $=3x=60$
Number of girls in the class $=2x=40$

Number of boys who are adults = $20\%$ of number of boys =$\frac{20}{100}\times 60=12$

Number of girls who are adults = $25\%$ of number of girls =$\frac{25}{100}\times 40=10$

Total number of boys and girls who are adults =$12+10=22$

Total number of boys and girls who are not adults = $100-22=78$

Percentage of boys and girls who are not adults =$\frac{78}{100}\times 100=78\%$.

so option $C$ is correct.