SOLUTION: if 2 1/2 cost $20, how much do 3 1/2 cost

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Question 632370: if 2 1/2 cost $20, how much do 3 1/2 cost
Answer by Edwin McCravy(8999) About Me  (Show Source):
You can put this solution on YOUR website!
if 2 1/2 cost $20, how much do 3 1/2 cost?
This one is more easily with decimals. Use 1/2 as .5
Consider the problem this way:

if 2.5 cost $20, how much do 3.5 cost?

2.5 is to $20 as x is to 3.5

2.5%2F20 = 3.5%2Fx

Cross-multiply:

(2.5)(x) = (20)(3.5)
    2.5x = 70
    2.5x%2F2.5 = 70%2F2.5
       x = $28

Edwin