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If there are 4 movies, all starting at 8:30, running continually throughout the day. One movie is 3 mins long, one is 18 mins, another is 24 mins. and the fourth is 12 mins. What is the next time (after 8:30) that all 4 movies will be starting at the same time?

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I don't see probability involved here. Anyway, what have you tried? Have you some guess? – leonbloy Oct 4 '12 at 14:53

Seconding the answer given by @Berci, at 9:42 all movies would start at the same time. This will happen a lot of times, but 9:42 is the next immediate time when they would start at the same time.

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Least common multiple(3,18,24,12) + 8:30 (minutes in modulo 60)

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