Question

Tick (✓) the correct answer:
A car takes 2 hours to reach a destination by travelling at 60 km/hr. How long will it take while travelling at 80 km/hr?
(a) 1 hr 30 min
(b) 1 hr 40 min
(c) 2 hrs 40 min
(d) none of these

Answer 1

(a) 1 h 30 min
Let x h be the time taken by the car travelling at 80 km/hr.

Speed (km/h)	60	80
Time (in h)	2	$x$

$$\begin{gathered} \mathrm{The}\mathrm{greater}\mathrm{the}\mathrm{speed},\mathrm{the}\mathrm{lesser}\mathrm{will}\mathrm{be}\mathrm{the}\mathrm{time}\mathrm{taken}. \\ \mathrm{So},\mathrm{it}\mathrm{is}\mathrm{a}\mathrm{case}\mathrm{of}\mathrm{inverse}\mathrm{proportion}. \\ \mathrm{Now},60\times 2=80\times x \\ \Rightarrow x=\frac{120}{80} \\ \Rightarrow x=1.5\mathrm{Therefore},\mathrm{the}\mathrm{car}\mathrm{will}\mathrm{take}1\mathrm{h}30\min \mathrm{to}\mathrm{reach}\mathrm{its}\mathrm{destination}\mathrm{if}\mathrm{it}\mathrm{travels}\mathrm{at}\mathrm{a}\mathrm{speed}\mathrm{of}80\mathrm{km}/\mathrm{h}. \end{gathered}$$