the wheels revolve round a common horizontal axis. they make 15, 20 and 48 revolutions in a minute respectively. starting with a certain point on the circumference down wards. after what interval of time will they come together in the same position?

the wheels revolve round a common horizontal axis. they make 15, 20 and 48 revolutions in a minute respectively. starting with a certain point on the circumference down wards. after what interval of time will they come together in the same position?