question_answer

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

A) 1 hour 

B) \[\text{1}\frac{1}{2}\]hours

C) \[2\frac{1}{2}\] hours   

D) 3 hours  

Correct Answer: D

Solution :

Tolling together for next time means tolling after the least possible seconds which is the L.C.M. of 9, 12 and 15. L.C.M. \[\text{=3}\times \text{3}\times \text{4}\times \text{5=180}\]minutes \[=\frac{180}{60}\]hours \[=3\]hours