algebra

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a disk jockey must play 14 commercial spots during one hour of radio show, each commercial is eiter 30 seconds or 60 seconds long. If the total commercial time during one hour is 11 minutes, then ow many 30 second commercials were played that hour?

  • algebra -

    x of 30 sec so (14-x) are 60 sec
    11*60 = 660 sec

    so
    30 x + 60(14-x) = 660

    870 - 30 x = 660

    30 x = 210

    x = 7

  • algebra -

    short commercial --- x
    long commercial ---- y

    x+y = 14 , #1
    30x + 60y =11(60)
    x + 2y = 22 , #2

    #2 - #1
    y = 8
    then x = 6

    6 shorts , 8 long

    check : 6+8 = 14
    30(6) + 60(8) = 180+480 = 660 = 11(60)

  • error 840 not 870 -

    x of 30 sec so (14-x) are 60 sec
    11*60 = 660 sec

    so
    30 x + 60(14-x) = 660

    840 - 30 x = 660

    30 x = 180

    x = 6

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