SOLUTION: A chainsaw runs on fuel that is 10% oil and 90% gas. How much oil will have to be added to 3 gallons of fuel that is 5% oil and 95% gas in order to use it in the chainsaw?

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Question 709509: A chainsaw runs on fuel that is 10% oil and 90% gas. How much oil will have to be added to 3 gallons of fuel that is 5% oil and 95% gas in order to use it in the chainsaw?
Found 2 solutions by stanbon, josgarithmetic:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
A chainsaw runs on fuel that is 10% oil and 90% gas. How much oil will have to be added to 3 gallons of fuel that is 5% oil and 95% gas in order to use it in the chainsaw?
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Equation:
oil + oil = oil
0.05*3 + 1*x = 0.10(3+x)
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5*3 + 100x = 10*3 + 10x
90x = 5*3
x = 1/6 gallon (amt. of pure oil needed for the mixture)
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Cheers,
Stan H.
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Answer by josgarithmetic(39617) About Me  (Show Source):
You can put this solution on YOUR website!
(amount of oil)/(amount of mixture)=(fraction as oil)

Using g for the amount of oil to add, amount of mixture is g+3. The "gas" (gasoline) is the part of ingredients that does not contain the oil.

%283%2A5%2Bg%29%2F%28g%2B3%29=10, using fractions as percents.
Solve for g.