Question

Find the present age of a boy whose age $12$ years from now will be the square of his present age.

• A. $5$ years
• B. $7$ years
• C. $4$ years
• D. $6$ years

Answer 1

Answer: (C)

$4$ years

Let $x$ be his present age.

Then,

$x+12=x^2$

$\Rightarrow x^2-x-12=0$

$\Rightarrow x^2-4x+3x-12=0$

$\Rightarrow x(x-4)+3(x-4)=0$

$\Rightarrow (x-4)(x+3)=0$

$\Rightarrow x=4$ or $x=-3$

As age cannot be negative so, the present age of the boy is equal to $4$ years.