Question

A train travels 40 km at a uniform speed of 30 kmph. Its average speed after travelling another 40 km is 45 kmph for the whole journey. Its speed in the second half of the journey is

• A. 45 kmph
• B. 90 kmph
• C. 60 kmph
• D. 75 kmph

Answer 1

The correct option is B

90 kmph

Let speed of the train in later half be x
Time taken to travel later 40 km = 40/x hours
Total time taken $=\frac{40}{30}+\frac{40}{x}$
Average speed = $\frac{Totaldistance}{Totaltime}=45$
$\frac{80}{\frac{40}{30}+\frac{40}{x}}=45$
$40x+1200=\frac{80}{45}\times 30x$

x= 90 kmph