Question

Three bells toll at interval of 9,12,15 min. It start together.,after what time they will meet

Answer 1

The LCM of

9 = 3x3

12 = 2x2x3

15 = 3x5

LCM = 2x2x3x3x5 = 180

So the three bells will toll together after every three minutes .

Answer 2

Minimum time required for heels to ring again together =LCM of given numbers.
LCM = product of highest exponents of every factors
= 3^2x2^2x5=180