Question

three bells tall at intervals of 9,12,15 min resp if they start talling together after whal time will they next tall together

Answer 1

HI !

Three bells toll at intervals of 9,12,15 min .
 If they start tolling together after what time will they next toll together ?

Ans :-

We have to find the LCM of 9 , 12 and 15

9 = 3 × 3
12 = 2 × 2 × 3
15 = 3 × 5

LCM = 3² × 2² × 5 = 180 

The three bells will start to toll together after 180 minutes 

Answer 2

See,

For finding the time, when all the bells will ring together, you will need the prior knowledge of the concept LCM(I assume you already know it).

Now, time after which the three bells will ring together will be the LCM of 9,12,15. This is because, we want to find the minimum time taken by the bell so that they ring together, even though they ring at different intervals.The LCM of the three numbers turns out to be 180 minutes.

Hence, the bells will ring together again after 180 minutes, or better say three hours.(1hr=60 minutes)

Cheers!