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a bag of marbles contains 5 red,7 green ,and some blue.if 1/3 of the marbles in the bag are blue,how many blue marbles are in the bag?

  • math -

    If there are only red, green and blue marbles in the bag, then given that 1/3 are blue, then red and green occupy 1-1/3=2/3 of the bag.
    Use direct proportion:

    2/3 bag : 5+7=12
    1/3 bag : X
    Cross multiply:
    x=(1/3)*12÷(2/3)
    =12/2
    = 6 (blue marbles)

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