LCM and HCF

Three wheels can complete 60, 36 and 24 rpm respectively. There is a red spot on each wheel that touches the ground at time zero. After how much time, all these spots will simultaneously touch the ground again?

Answer:

60 rpm = 1 rps

36 rpm = 36/60 rps = 0.6 rps

24 rpm = 24/60 rps = .4 rps

LCM of 1, 0.6 and 0.4 = 6

So, after 6 rounds of 1^st tyre, 10 rounds of 2^nd tyre and 15 rounds of third tyre, all will meet.

Time taken for 6 rounds of 1^st tyre = 6 secs.

So, all three tyres will meet after 6 secs