This is a problem from Test of Mathematics, TOMATO Objective 8, useful for ISI and CMI Entrance. Try out this problem. (by Rahul Roy)
Problem: Two trains of equal length L,travelling at speeds v1 and v2 miles per hour in opposite directions,take t seconds to cross each other .then L in feet is:
Total distance required to cover by one train is 2L.
By considering one train at rest then speed of other train is v1+v2.
converting into feet we get
L = 11(v1+v2)T 15