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 the increased speed be x km/h.

Time (in h)	10	8
Speed (km/h)	48	x+48

$$\begin{gathered} \mathrm{Since}\mathrm{speed}\mathrm{and}\mathrm{time}\mathrm{taken}\mathrm{are}\mathrm{in}\mathrm{inverse}\mathrm{variation},\mathrm{we}\mathrm{get}: \\ 10\times 48=8\left(x+48\right) \\ \Rightarrow 480=8x+384 \\ \Rightarrow 8x=480-384 \\ \Rightarrow 8x=96 \\ =12 \\ \mathrm{Thus},\mathrm{the}\mathrm{speed}\mathrm{should}\mathrm{be}\mathrm{increased}\mathrm{by}12\mathrm{km}/\mathrm{h}. \end{gathered}$$