between two stations a train accelerates uniformly at first then moves with constant speed and finally retards uniformly.if the ratio of time taken are 1:8:1 and the greatest speed is 60km/hr , what is the avg speed over the whole journey ? In this question, why do we take total time as 10t? can anyone help?

See the average velocity is the ratio of total distance and total time. Since the ratio of times are 1:8:1. If the proportionality constant is k then t1= k t2= 8k and t3= k so the total time is 10k and the total distance is the area of trapezium = 1/2 (8k+10k)* 60= 540k so the average velocity is 540k/10k = 54 km/hr