SOLUTION: The fuel for a certain two cycle engine is a mixture of 8 parts gasoline and 2 parts oil. How many gallons of gas are needed to make 20 gallons of fuel?

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Question 23246: The fuel for a certain two cycle engine is a mixture of 8 parts gasoline and 2 parts oil. How many gallons of gas are needed to make 20 gallons of fuel?
Found 2 solutions by Paul, rapaljer:
Answer by Paul(988) About Me  (Show Source):
You can put this solution on YOUR website!
8/3=20/x ---> cross multiply
8x=20 x 2
8x=40
x=5
Hence, 5 gallons of gas are needed to make 20 gallons of fuel.

Answer by rapaljer(4671) About Me  (Show Source):
You can put this solution on YOUR website!
Set up a ratio of gas to total fuel. 8 parts gas + 2 parts oil = 10 parts total fuel.

Let x = number of gallons of gas needed to make 20 gallons of fuel.
%28gas%29%2F%28total%29+=+8%2F10=+x%2F20

Remember a%2Fb=c%2Fd means that ad=bc

In the same way, 8%2F10=+x%2F20 means that 8%2A20=10%2Ax
10x = 160
x= 16 gallons

You can do it in your head without an equation if you like. Just think about the ratio of 8 gallons of gas to 10 gallons total. The 20 gallons total is exactly twice as much as the 10 gallons, so the gas will be exactly twice the 8 gallons or 16 gallons. However, it usually doesn't work out this nicely. That's why I like to do it with the ratio and equation.

R^2 at SCC