A temple has five bells which ring at intervals of 12, 15, 16, 20 and 25 minutes respectively. If they ring together at midnight, at what time will they next ring together?
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 8:00 p.m.
Each bell rings at multiples of its own interval, so all five ring together again after the LCM of the intervals.
\(12=2^{2}\times3\), \(15=3\times5\), \(16=2^{4}\), \(20=2^{2}\times5\), \(25=5^{2}\)
LCM \(=2^{4}\times3\times5^{2}=1200\) minutes
1200 minutes \(=20\) hours
Midnight \(+\) 20 hours \(=\) 8:00 p.m.
The bells next ring together at 8:00 p.m.