Question

Three bells, A,B and C toll every 5 seconds, 8 seconds and 12 seconds respectively. They all start tolling together. After how many seconds will they all toll together again

Answer 1

120 seconds

Explanation:

To obtain the number of seconds they will all till together again, obtain the lowest common multiple of the three bell times :

Bell A :

Multiples of of 5 = 5, 10, 15, 20, 25, 30, 35, 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, 95, 100, 105, 110, 115, 120, 125

Bell B :

Multiples of 8 = 8, 16, 24, 32, 40, 48, 56, 64, 72, 80, 88, 96, 104, 112, 120, 128

Bell C :

Multiples of 12 = 12, 24, 36, 48, 60, 72, 84, 96, 108, 120, 132

From the values above, the lowest common multiple is 120, Hence, they'll toll together again after 120 seconds