Question

on earth 120 kilometre track A train travels the first 30 kilometre at a speed of 30 kilometre per hour how fast the train travel over the next 90 kilometres so as the average 30 kilometre per hour for the entire trip ​

Answer 1

30 kmph.

There is a logical shortcut for this question.

If the average is equal to the first part, and the second part is asked, the second part should also be equal to the average. Think about that.

But as a more formal solution:

Time to cover 120 km with average speed 30 kmph = 4 hours.

Time to cover 30 km at speed 30 kmph = 1 hour.

To cover the remaining 90 km, time elapsed must be 4 hours - 1 hour = 3 hours.

So, speed for the second part = 90 km / 3 hours = 30 kmph.