Three bells commence tolling together and toll at intervals of 1, 3 and 5 seconds respectively. In 10 minutes, how many times do they toll together ?
Choose the correct option.
A) 39
B) 40
C) 41
D) 42
E) 43
LCM of 1, 3 and 5 is 15.   So, after each 15 seconds, they would toll together.   Hence, in 10 minutes, they would toll 10*60 seconds / 15 seconds = 40 times   But then the question says they commence tolling together. So, they basically also toll at thebeginning(0second).   So, total tolls together = 40+1= 
<gadget id="calculator">40+1</gadget>
<output>41</output>
41   Answer 41
<result>C</result>
Three bells commence tolling together and toll at intervals of 1, 3 and 5 seconds respectively. In 10 minutes, how many times do they toll together ?