Question

Rohan is 3 years older than his sister Ruhi. If the product of their age is 40, then Ruhi's age is ___

• A. 4 years
• B. 8 years
• C. 9 years
• D. 5 years

Answer 1

The correct option is D

5 years

Let Ruhi's age be $x$

Rohan's age = $x+3$

Product of their age = 40

Therefore

$x\times (x+3)=40$

$\Rightarrow x^2+3x-40=0$

$\Rightarrow x^2+8x-5x-40=0$

$\Rightarrow x(x+8)-5(x+8)=0$

$\Rightarrow (x+8)(x-5)=0$

$\Rightarrow x=-8,5$

Since age cannot be negative, Ruhi's age is 5 years.