Question

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

• A. $21$ years
• B. $18$ years
• C. $12$ years
• D. $9$ years

Answer 1

The correct option is D $9$ years

Given : Average age of three boys is $15$ years.
$\therefore$ Sum of ages of three boys $=15\times 3=45$ years

Let the ages of the three boys be $3x,5x$ and $7x.$
Then, $(3x+5x+7x)=45$
$\Rightarrow 15x=45$
$\Rightarrow x=3$
So, age of the youngest boy $=3x=3\times 3=9$ years