<PRE><B>Question 750562</B>
Three bells ring at the interval of 10,15 and 20 minutes respectively .
 If they all ring at 11 a.m at once,what time they ring together again ?
:
Find the least common multiple of 10, 15, 20, 
Prime factor
10: 2*5
15: 3*5
20: 2*2*5
then
2*2*3*5 = 60 is LCM
:
60 min from 11 is 12
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