# 4 bells toll together at 9 am.they toll after 7,8,11 and 12 seconds respectively .how many times will they toll together again in the next 3 hrs? pls tell me the steps to do this sum pls answer fast friends

1
by mssrinidhi

2015-03-24T23:25:18+05:30

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Bell1 : tolls at  t = 0seconds, 7s, 14s, 21s....
2"                  0s, 8s, 16s, 24s,...
3:  0,11,22, 33s,...
4:  0, 12, 24,36,48s,...

LCM of 7s , 8s ,11s ,12 is :  7 * 2 *2*2 *11 * 3 = 1848 sec = 30 min and 48 seconds.
so we add 30 m 48 sec to the previous time instant that they tolled together.

next time all the bells will toll together will be at  9 h 30min 48 sec
next time it will be  10 h 1 min 36 sec
next it will be at  10 h 32 min 24 sec
next it will be  at  11 h  3 min 12 sec
next it will be at    11 h  34 min 0 sec
next it will be at  12 h  04 min 48 sec..  this is after 3 hrs from 9 am.

===>  to do it simply:  in 180 minutes = 3 hrs,  they toll together
=  180 min / 30min 48sec  times
=  5.84  times  that is  5 times.