An express train travelled at an average speed of 100 km/hr, stopping for 3 minutes after every 75 km. How long did it take to reach its destination 600 km from the starting point ?

Answer: Option A

Time taken to cover 600 km
$$\begin{array}{rl}& =\left(\frac{600}{100}\right)hr\\ & =6hrs\end{array}$$
Number of stoppages
$$\begin{array}{rl}& =\frac{600}{75}-1\\ & =7\end{array}$$
Total time of stoppages
= (3 × 7) min
= 21 min
Hence, total time taken = 6 hrs 21 min