Question

A train travels 20 km at a uniform speed of 60 km/h and next 20 km at a uniform speed of 80 km/h calculate its average speed.

Answer 1

Given,

Distance traveled = 20 km

Speed = 60 km/h

So, $timetaken=\frac{Distance}{Speed}=\frac{20}{60}=\frac{1}{3}h$

For the next journey

Distance traveled = 20 km

Speed = 80 km/h

So, $timetaken=\frac{Distance}{Speed}=\frac{20}{80}=\frac{1}{4}h$

Now,

Total distance traveled = 20 + 20 = 40 km

Total time taken = $\frac{1}{3}+\frac{1}{4}=\frac{7}{12}$

We know,

$Averagespeed=\frac{Totaldistancetraveled}{Totaltimetaken}=\frac{40}{\frac{7}{12}}=68.5$ km/h

Hence the average speed of the train is 68.5 km/h