<PRE><B>Question 782047</B>
two train 120m and 80m in length are running in opposite direction with velocity 40 km/hr and 30km/hr. in what time they will completely cross each other


the sum of lengths of the trains is the distance 

120 + 80 = 200 m
=0.2 km

the trains are in opposite direction so effective speed = 40+30=70 km/h

t= d/r

t=0.2/70

t=0.00286 hours

1 hour = 3600 seconds

0.00286 * 3600 = 10.29 seconds</PRE>