Question 465792
You can solve this using a proportion, which basically means a fraction = a fraction.  For both, I'm going to put the number of miles over the number of gallons; if you want, you can put gallons over miles as long as you do it both times.  {{{408/15=340/x}}}.  My favorite way to solve this is to do cross multiplication: multiply the top left with the bottom right, and multiply the bottom left with the top right.  {{{408*x=15*340}}}.  Simplify: {{{408x=5100}}}.  Divide by 408 on both sides to get x by itself, and your final answer is {{{x=12.5}}}.


I like to go back and check by doing the division on both sides and making sure I get the same thing for both: {{{408/15=27.2}}} and {{{340/12.5=27.2}}}.  Both fractions equal 27.2, so we're definitely right!