Q. Four Bells commence tolling together and toll at the intervals of 3, 9, 12, 15 seconds respectively. In 30 minutes time, how many times will they toll together ?
✅ Correct Answer: (B)
11
Explanation:
Find the LCM of 3, 9, 12, 15.
3 = 3
9 = 3²
12 = 2² × 3
15 = 3 × 5
LCM = 22×32×5=180 seconds.
Bells toll together every 180 seconds (i.e., every 3 minutes).
Total time = 30 minutes = 1800 seconds.
1800180=10
Add 1 for the initial toll at time zero.
10+1=11
Answer: 11
Explanation by: Mr. Dubey
Find the LCM of 3, 9, 12, 15.
3 = 3
9 = 3²
12 = 2² × 3
15 = 3 × 5
LCM = 22×32×5=180 seconds.
Bells toll together every 180 seconds (i.e., every 3 minutes).
Total time = 30 minutes = 1800 seconds.
1800180=10
Add 1 for the initial toll at time zero.
10+1=11
Answer: 11