Three bells are ringing at intervals of 20, 30 and 40 minutes respectively. At what time will they ring together again, if they ring simultaneously at 9 a.m?

Three bells are ringing at intervals of 20, 30 and 40 minutes respectively. At what time will they ring together again, if they ring simultaneously at 9 a.m?

Explanation

Find LCM of 20, 30, and 40:

Prime factors:

20 = 2² × 5

30 = 2 × 3 × 5

40 = 2³ × 5

LCM = 2³ × 3 × 5 = 120 minutes

120 minutes = 2 hours, so if they ring together at 9:00 am, they will ring together again at 11:00 am.