Alarms from three clocks sound every 2, 4 and 6 hours respectively. If started together, how many times do all three ring together in 3 days?

1. The alarms coincide at the LCM of 2, 4, 6 = 12 hours. 2. 3 days = 72 hours. 3. Multiples of 12 within 72 (at 12, 24, 36, 48, 60, 72) = 6 times. _Source: RRB Group D CEN-02/2018 PYQ, Q.96._