Management Aptitude Test Sep 2011 Paper

(1) Let original speed of the car = x km /h
Then, according to the question,
$\frac{715}{\mathit{x}}-\frac{715}{\mathit{x}+10}$ = 2
⇒ 715 (x + 10 - x) = 2x (x + 10)
⇒ 715 x 5 = x (x + 10)
⇒ ${\mathit{x}}^2$ + 10x - 3575 = 0
x =$\frac{-10\pm \sqrt{100+14300}}{2}$
⇒ x = $\frac{-10+120}{2}$
⇒ x = $\frac{110}{2}$ = 55 km/h (taking positive sign)