Question

three bells toll at intervals of 9,12,15 minutes respectively . if they start tolling togeather ,after what time will they next toll together.

Answer 1

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......................

Answer 2

in  order to get answer u should calculate lcm
lcm of 9,12 and 15
 = 180
therefore ,after 180 minutes they will toll together.