Question

A train moving at a uniform speed of 60 km/h covers a distance of 30
km. It covers another distance of 40 km at a uniform speed of 70 km /
h. Calculate the average speed of the train.

Answer 1

Explanation:

Time taken in first half=Distance/Time=30/60=1/2 hr

Time taken in second half=40/70=4/7 hr

Average speed=Total Distance/Total time taken

$\tt \dashrightarrow \: \frac{30 + 40}{ \frac{1}{2} + \frac{4}{7} } \\ \\ \tt \dashrightarrow \frac{70}{ \frac{7 + 8}{14} } \\ \\ \tt \dashrightarrow \: \frac{70}{ \frac{15}{14} } \\ \\ \tt \dashrightarrow \: \frac{70 \times 14}{15} \\ \\ \tt \dashrightarrow \: \frac{196}{3} \\ \\\tt \dashrightarrow 6 5\frac{1}{3} \: kmph$