Four bells begin to toll together and then each one at intervals of 6 s, 7 s, 8 s and 9 s respectively. The number of times they will toll together in the next 2 hr is:
Op 1: 14 times
Op 2: 15 times
Op 3: 13 times
Op 4: 11 times

Question

Four bells begin to toll together and then each one at intervals of 6 s, 7 s, 8 s and 9 s respectively. The number of times they will toll together in the next 2 hr is:
Op 1: 14 times
Op 2: 15 times
Op 3: 13 times
Op 4: 11 times

anonymous · Answer

take lcm of the seconds

anonymous · Answer

least common multiple is 
$$2^3\times 3^2\times 7=504$$ so they chime together every $504$ seconds

anonymous · Answer

there are $2\times 60\times 60=7200$ seconds in two hours
divide

kc_kennylau · Answer

wow i'm imagining the situation, so funny xD

anonymous · Answer

ya got it . thank you.