SOLUTION: A contractor has a 12-poind mixture that is one-fourth cement and three-fourths sand. How much of a mixture that is half sand needs to be added to produce a mixture that is one-thi

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Question 947780: A contractor has a 12-poind mixture that is one-fourth cement and three-fourths sand. How much of a mixture that is half sand needs to be added to produce a mixture that is one-third cement?

I cannot figure out how to set this up at all
Answer by MathLover1(20850) About Me  (Show Source):
You can put this solution on YOUR website!

A contractor has a 12-poind mixture that is one-fourth cement and three-fourths sand. How much of a mixture that is half sand needs to be added to produce a mixture that is one-third cement?
We can write an equation based on the amt of cement
let x be amount of half cement mixture required
%281%2F4%2912%29%2B+%281%2F2%29x+=+%281%2F3%29%28x%2B12%29

Multiply equation by 12+to get rid of the denominators

3%2812%29+%2B+6x+=+4%28x%2B12%29
36+%2B+6x+=+4x+%2B+48
6x+-+4x+=+48+-+36
2x+=+12
x+=+6-> lb of the half cement mixture