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Math

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a disc jockey must play 14 commercial spots during 1 hour of a radio show.Each commercial is either 30 seconds or 60 seconds long. If the total commercial time during 1 hour is 11 min, how many 30-second commercials were played that hour. How many 60-second commercials.

  • Math - ,

    11 min * 60 s/min = 660 s,

    x - 30 s comm,
    y - 60 s comm,
    x + y = 14 comm,
    y = 14 - x,

    30x + 60y = 660 s,
    Substitute 14 - x for y:
    30x + 60(14 - x) = 660,
    30x + 840 - 60x = 660,
    -60x = 660 - 840
    -30x = -180,
    x = 6 30 s comm,
    6 + y = 14,
    y = 8 60 s comm.

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