Question

Four bells ring at interval of 5, 10, 15 and 20
minutes. If they ring together at 9:00 AM, at
what time will they ring together again?
(A) 10:00 AM (B) 10:30 AM
(C) 11:00 AM
(D) 11:30AM​

Answer 1

Answer:

(A) 10:00 AM

Step-by-step explanation:

In simple way, we need to find the lowest number, which is fully divisible by 5, 10, 15 and 20. So let's find the LCM of these 4, and that is 60mins.

So 60 minutes after 9 o'clock, all 3 bells will ring together again, ie at 10 o'clock.

Another way, non math way, to solve this is

Bell A will ring at 9:00, 9:05, 9:10, 9:15, 9:20, 9:25, 9:30, 9:35, 9:40, 9:45, 9:50, 9:55, 10:00

Bell B will ring at 9:00, 9:10, 9:20, 12:30, 9:40, 9:50, 10:00

BellC will ring at 9:00, 9:15, 9:30, 9:45, 10:00

BellD will ring at 9:00, 9:20, 9:40, 10:00

So, after ringing together at 9 o'clock, the bells will again ring together at 10 o'clock.

Answer 2

option A is correct ans 10:00 AM