Question

A and B started from X and Y respectively at the same time in the opposite directions. After meeting, A took 2.7 hours to reach Y and B took 1.2 hours to reach X. If the speed of B is 48 km/h, what is the speed of A(in km/h)?

Answer 1

Answer:

Let speed of Train B = x

120/x= √(9/16)

=> x = 4 x 120/3 = 160 km/hr

Note : This can be solved without using this formula by using fundamentals of Time, Speed & Distance.

Derivation of formula :

Let x be the total distance and t be the time at which the two trains meet.

Let s1, s2 are speeds of train A, train B respectively and a & b are the times at which they reach the destination after they meet.

x = t(s1 + s2) ...(1)

x = (t + a)s1 ...(2)

x = (t + b)s2 ...(3)

Solving (1), (2) & (3)

t = √(a*b)

=> Time to meet is the Geometric Mean of individual time after meeting.

=> s1/s2 = √(b/a)

:-)