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5 November, 21:22

There is a string of red and blue lights strung around a window. The red lights blink every 3 seconds, and the blue lights blink every 5 seconds. How many times will they blink at the same time in one minute?

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Answers (2)
  1. 5 November, 22:23
    0
    To answer this question, we need to determine how many common multiples there are between 3 and 5, that are lower than 60.

    It turns out that every common multiples of 3 and 5 is also a multiple of 15. So, there are (60/15) = 4 such common multiples.

    So the answer is 4.

    Here is a more detailed description:

    After 1 seconds:

    The red lights don't blink

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    They have blinked at the same time 1 times

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    They have blinked at the same time 2 times

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    The red lights blink

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    They have blinked at the same time 3 times

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    After 60 seconds:

    The red lights blink

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    They have blinked at the same time 4 times
  2. 5 November, 22:41
    0
    they will blink 4 times at the same time in one minute

    Step-by-step explanation:

    you have to find the least common multiple of 5 and 3

    LCM of 5,3 = 15

    So, the two lights will blink together every 15 seconds.

    No. of times blinking together in one minute = 60/15 = 4
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