Question

A subject conference is scheduling 20-minute sessions and 25-minute sessions with 10 minutes between sessions. The sessions at the conference begin at 8 A.M. What is the next time at which all sessions will begin at the same time again?

Answer 1

30=2*3*5 and 35=5*7, then the least common multiple is 2*3*5*7=210 minutes. This means that 7 20-minutes sessions with 10-minutes breaks and 6 25-minutes sessions with 10-minutes breaks will end together after 210 passed minutes and at 11:30 A.M. all sessions will begin at the same time.