Two trains A and B start at uniform speeds, simultaneously from two stations P and Q, respectively, towards each other. After crossing each other, A takes 20 hours to reach Q and B takes 5 hours to reach P. If train A is moving at a speed of 55 km/h, the speed of B (in km/h) is:

Let the speed of train A be S
A
​
and the speed of train B be S
B
​
.
Let the time taken by A to reach its destination after crossing be T
A
​
, and by B be T
B
​
.

Given:
S
A
​
=55 km/h
T
A
​
=20 hours
T
B
​
=5 hours

We know the standard relation for two objects moving towards each other meeting and continuing to their destinations:

S
B
​

S
A
​

​
=
T
A
​

T
B
​

​


​

Substituting the given values:

S
B
​

55
​
=
20
5
​


​

S
B
​

55
​
=
4
1
​


​

S
B
​

55
​
=
2
1
​

S
B
​
=55×2=110 km/h