Homework Help: math

Posted by shank on Sunday, May 1, 2011 at 7:53pm.

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 - MathMate, Sunday, May 1, 2011 at 8:21pm
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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