Question

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

Options

• 1 hour

• \[1\frac{1}{2}\] hours
• \[2\frac{1}{2}\] hours

• 3 hours

Answer 1

3 hours
The L.C.M. of 9, 12, and 15 will give us the minutes after which the bells will next toll together.

L.C.M. = 2² × 3² × 5
= 180
So, the bells will toll together after 180 min.
On converting into hours:
180/60 = 3 hours