Question

A car takes 5 hours to reach a destination by travelling at the speed of 60 km/hr. How long will it take when the car travels at the speed of 75 km/hr?

Answer 1

Let x h be the required time taken. Then, we have:

Speed (in km/h)	60	75
Time (in h)	5	x

Clearly, the higher the speed, the lesser will be the the time taken.
So, it is a case of inverse proportion.
$$\begin{gathered} \mathrm{Now},60\times 5=75\times x \\ \Rightarrow x=\frac{60\times 5}{75} \\ \Rightarrow x=4 \end{gathered}$$

Therefore, the car will reach its destination in 4 h if it travels at a speed of 75 km/h.