6 bells commence tolling together and toll of intervals are 2, 4, 6, 8, 10 and 12 s, respectively. In 1 h, how many times, do they toll together?

LCM of 2, 4, 6, 8, 10, 12 =(2 x 2 x 3 x 2 x 5) = 120 ∴ After every 2 min, they toll together. ∴ Number of times they toll together in one hour = (60/2) + 1 times = 31 times