Question

Three bells toll at intervals of 9, 12 and 15 minutes respectively. All the three begin to toll at 8 a.m. At what time will they toll together again?

Answer 1

First find Lcm of 9, 12, 15 which is
9 = 3 × 3
12 = 2 × 2 × 3
15 = 3 × 5
Then multiply
LCM (9, 12, 15) = 3 × 3 × 2 × 2 × 5
LCM (9, 12, 15) = 180 minutes
therefore it will till after 180 mins
Which is 11 am
Thanx

Answer 2

Find the prime factors:

9 = 3²

12 = 2² x 3

15 = 3 x 5

Find the LCM:

LCM = 2² x 3² x 5 = 180 mins

Convert mins to hours:

180 mins = 180 ÷ 60 = 3 hours

Find the time it will right together again:

8 am + 3 hours = 11 am

Answer: It will bring together at 11am