Five bells begin to toll together and toll respectively at intervals of 6, 7, 8, 9 and 12 seconds. How many timesthey will toll together in one hour?
L.C.M. of (6,7,8,9,12) = 504
Thus, after every 504 seconds = 8.4 minutes, the bells toll together.
=> Number of times, they will toll together in an hour = $$\frac{60}{8.4}=7.14=$$ 7 times
=> Ans - (D)