Question

A car can finish a certain journey in 10 hours at the speed of 48 km/hr. By how much should its speed be increased so that it may take only 8 hours to cover the same distance ?

Answer 1

Let x km/hr be the speed. Then
$\begin{array}{ccc}\text{Time (in hours)}& 10& 8\\ \text{Speed (in km/hr)}& 48& x\end{array}$
Last period, more speed
$\therefore$ By inverse variation
$10:8=x:48\Rightarrow \frac{10}{8}=\frac{x}{48}\Rightarrow 8x=10\times 48\Rightarrow x=\frac{10\times 48}{8}=60$
$\therefore$ Speed requird = 60 km/hr.
Already speed = 48 km/hr.
$\therefore$ Speed to be increase = 60-48=12 km/hr