Two model trains begin at the toy train station and travel continuously on two circular tracks of equal length. The first train completes a circuit in 20 seconds and the second train in 15 seconds. If both trains, leave the station at the same time, after how many seconds will the two trains first meet again?

Question

Answer is 60 seconds, but I don't know did they get it. Please show me the calculation please. Thanks

Answer 1

20 = 4*5
15 = 3*5

LCM(15,20) = 3*4*5 = 60

every 60 seconds one train does 3 laps, and other does 4 laps.