Two trains running in opposite directions cross a man standing on the platform in 27 seconds and 17 seconds respectively and they cross each other in 23 seconds. The ratio of their speeds is ?

Solution : 

L1=27x........(i)

L2=17y.........(ii)

Also, 

L1+L2=23(x+y).........(iii)

So, 
27x+17y=23(x+y)

X/y=3/2 or x : y = 3 : 2 Ans