Question

The average age of $3$ girls is $20$ years and their ages are in proportion $3:5:7,$ the age of youngest girl is ___.

• A. $8$ years $3$ months
• B. $6$ years $8$ months
• C. $12$ years
• D. $20$ years

Answer 1

The correct option is C $12$ years

Given that the ages of girls are in proportion $3:5:7$

So, we can say that their ages are $3x,5x$ and $7x$

Also, average age of $3$ girls $=20$ years

$\Rightarrow \frac{3x+5x+7x}{3}=20$

$\Rightarrow 5x=20$ i.e. $x=4$

$\therefore$ Age of youngest girl $=3\times 4=12$ years