Problems on LCM

Now Lets take a look at  below problem.

1. Ram takes 3 mins to complete one round on a circular track. Raghu takes 6 mins to completed one round on the same circular track. At what time Ram and Raghu cross each other on the track?

Sol:

Ram    takes 3 mins to complete one round.
Raghu takes 6 mins to complete one round.

Consider dotted lines as time.
Ram    ............................... (1st round Completed in 3 mins)
Raghu ............................... (1/2 round Completed in 3 mins)

Ram   ...............................(2nd round Completed in 6 mins)
Raghu ...............................(1st round Completed in 6 mins)

That means , Ram and Raghu cross each other in 6 mins.

6 mins is nothing but the least time at which Ram and Raghu cross eachother for first time on the circular track.
LCM (3,6) is 6.

2.) How many times both Ram and Raghu cross each other in one hour?

Sol: Since for every 6mins they cross each other one time.
For 60 mins (1 hour) they cross 10 times.