Six bells start ringing together and ring at intervals of 4, 8, 10, 12, 15 and 20 seconds respectively. How many times will they ring together in 60 minutes ?	Choose the correct option.
A) 5  B) 11  C) 21  D) 31  E) 32
LCM of 4, 8, 10, 12, 15 and 20 = 120 seconds = 2 minutes   That means All the six bells will ring together in every 2 minutes   Number of times they will ring together in 60 minutes =1+60/2= 
<gadget id="calculator">1+60/2</gadget>
<output>31</output>
31   Answer :31
<result>D</result>
Six bells start ringing together and ring at intervals of 4, 8, 10, 12, 15 and 20 seconds respectively. How many times will they ring together in 60 minutes ?