Question

Three bells ring at intervals 9,12,15 minutes respectively. if they start ringing together, after what time will they next ring together again​

Answer 1

Answer:

I think it is after 2 mins

Answer 2

Answer:

180 mins

Step-by-step explanation:

let 3 bells be

b1

b2

b3

intervals of b1,b2 and b3 = 9 , 12 and 15 min

the next time they will ring together = lcm of 9,12,15

how do I know it is lcm not hcf?

a simple trick to know if it is lcm or hcf we have to take check the value of answer, if answer will be greater than the given values then it is lcm, if answer will be smaller than given values then if is hcf.

obviously answer in this would be greater than the given values

so we take lcm.

so lcm of 9,12 and 15 is 180

so after 180 mins they will again ring together as u see in picture