Hey, Math Central!
I need help with a question, please. It's a middle level, and I am a student. Thanks.

George's car gets 3 more miles per gallon during highway driving that it does during city driving. Recently he drove 112 miles on a highway and 150 miles in the city and used exactly 10 gallons of gas. How many miles per gallon does his car get during city driving??

Thank you very much!



Let c = the number of city miles George gets per gallon. Then if he drives 150 miles in the city, his car burns 150/c gallons doing so.

Now let h = the number of highway miles George gets per gallon. If he drives 112 miles on the highway, he uses 112/h gallons doing so.

But you are told that h = c + 3, so let's substitute "c + 3" in place of the "h". So George's car burns 112/(3 + c) gallons on the highway.

Since George used up 10 gallons in all for his trip, then you know that
150/c + 112/(3+c) = 10.

Now you have an equation with just one variable in it. Re-arrange it to solve for c - that's the answer you are seeking.

Hope this helps,
Stephen La Rocque>