Question

The average age of three boys is $15$ years. If their ages are in the ratio $3:5:7$, the age of the youngest boy is

• A. $21$ years
• B. $18$ years
• C. $15$ years
• D. $9$ years

Answer 1

The correct option is D $9$ years

Let age of three boys be $=3x,5x$ and $7x$
ATQ
$\frac{3x+5x+7x}{3}=15$
$\frac{15x}{3}=15$
$x=3$
youngest Boy $=3\times 3=9year$.