Question

on a 120 km track a train Moves the first 30 km at a uniform speed of 30 km per hour how much how fast much the train travel in next 90km so the average speed 60 km per hour for the entire trip

Answer 1

Let's assume that the train should run with the speed of S for next 90 km to achieve avs speed of 60km/hr

avg speed = (total distance covered)/(total distance travelled)
60=120/((30/120)+(90/S))
(30/120)+(90/S) = 120/60
(90/S) = 2-(1/4) = 7/4
S/90=4/6
S=(4x90)/6
S=360/6
S=60 km/hr