Answers

2016-04-30T14:36:19+05:30
For this you should calculate their lcm i.e. the lowest common multiple

lcm of 9,12 and 15 = 180

so,after 180min i.e. 3hrs they'll toll together......................
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2016-04-30T14:56:38+05:30
In  order to get answer u should calculate lcm
lcm of 9,12 and 15
 = 180
therefore ,after 180 minutes they will toll together.
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