Four bells toll at an interval of 8,12,15 and 18 seconds respectively. all the four bells begin to toll together. how many will they toll together in one hour excluding the one at the start?

The nest time they toll together is given by the LCM of  8,12,15 and 18 

8= 2*2*2
12=2*2*3
15 = 3*5
18=2*3*3 

LCM = 2*2*2*3*3*5 = 360

so they will toll together every 360 seconds

So in hour hour they will toll 3600/360 = 10 times Answer