A train starts from A at 6 AM andreaches B at 11 AM on the same day. Anothertrain starts from B at 8 AM and reaches A at 3 PM on the same day. At what time the two trains will have crossed each other?

9:45 AM

Since, the first train that travels from A to B covers the distance D in 5 hour

Since, the second train that travels from B to A covers the distance D in 7 hour

So , Ratio of          A       B

Time                     5   :   7

Speed                   7   :   5   

( Speed is inversely proportional to time )

LCM of ( 7,5) = 35 km

A alone travels till 8:00 am . so , Distance traveled by A in 2 hours

= 7 × 2 = 14 km

Remaining Distance = 35 - 14 = 21 km

Let Speed of A = 7 km/h & Speed of B = 5 km/h

Relative speed when moves in opposite direction = 7 + 5 = 12 km/h

Time = \(\frac{Distance}{Speed}\)

= \(\frac{21}{12}\)

= 1.75

= 1 hour 45 minutes

So , They will cross each other at = 8:00 am + 1 hour 45 minutes 

= 9:45 am