First take lcm of 2,4,6,8,10,12=120
therfore toll altogether at same time is 120sec
how many tolls in 30 minutes=1800sec=?
but in the question
six bells commence tolling together(first toll) and tolls at intervals of 2,4,6,8,10,12,
beginning itself tolling from.so we should consider that toll also
therfore 15 times+1 time=16 times