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Math

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Three lighthouses on three nearby islands flash their lights every evening. On one island, the light flashes every 45 seconds. The lighthouse on the second island flashes every 2 minutes. The third lighthouse flahses a light every 1 and 1/4 minutes. Suppose the lights flash together at 8:35pm. At what time will they flahs together agian? Explain your answer.

  • Math -

    First the times in seconds.
    Then least common multiple
    45 seconds, 120 seconds, 75 seconds
    factor them all
    3 *3 * 5
    2 * 2 * 2 * 3 * 5
    3 * 5 * 5
    so we need
    2 * 2 * 2 * 3 * 5 * 5
    thet is
    8*3*25
    =600 seconds
    = 10 minutes

  • Math -

    8:45

  • Math -

    It's actually 2*2*2*3*3*5*5 = 1800 seconds which is 30 minutes. It will be 9:05 when they all flash together again.

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