SOLUTION: Hi! This is a problem from me test. I really need help. Thank you On a trip Jennifer noticed that her car averaged 21mi/gal of gas except for the days she used the air conditionin

Algebra ->  Customizable Word Problem Solvers  -> Travel -> SOLUTION: Hi! This is a problem from me test. I really need help. Thank you On a trip Jennifer noticed that her car averaged 21mi/gal of gas except for the days she used the air conditionin      Log On

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Question 512387: Hi! This is a problem from me test. I really need help. Thank you
On a trip Jennifer noticed that her car averaged 21mi/gal of gas except for the days she used the air conditioning, and the it averaged only 16mi/gal. If she used 91 gal of gas to drive 1751 mi, how many of those miles did she use the air conditioning?
Answer by Sarah900(12) About Me  (Show Source):
You can put this solution on YOUR website!
(mileage with AC (mi/gal))*(gas used with AC(gal))+ (mileage without AC (mi/gal))*(gas used without AC(gal))=total miles traveled (miles)
Note how the units cancel out to leave you with miles
Assign x for one of the missing elements. We'll say the gas Jennifer used when she was using AC= x. Since she used 91 gallons total the expression that would tell you what she used without AC= 91-x.

Plug in what you know and solve for x
(21)*(x)+(16)*(91-x)=1751
21x+1456-16x=1751
5x+1456=1751
5x=295
x=59

So she used 59 gallons when she had AC. To find how much she used without
91-59=32

You can find how many miles she drove during each by multiplying the mileage with the corresponding number of gallons. So...
21*59=1239
16*32=512