How much would gas cost for 374 mi in a car that gets 18 mi to the gallons?

Answer 1

Of course you need to know how much gas costs in this instance, but let's assume $3 per gallon:

First setup the equation to cancel units:

(1 gallon / 18 miles) * (374 miles) * (3 dollars / 1 gallon)

Check: are we left with dollars? we gallons on top of one fraction, and on the bottom of another, so gallons cancel; same for miles. So we are left with dollars, and numerically we have 1/18 * 374 * 3 dollars and that gives us:

$63.33

You should be able to see that now that I've done the work of putting the units in the fractions in the right order, you need only change the numerical part to input a real price-per-gallon; so if 18 mpg and 374 mi are constant, you can take 374/18 = 20.778 and multiply that by whatever the price per gallon is. Notice how the further you travel, the more important every penny is in the price per gallon. So when it comes to a choice of fuel grade or even which gas station to go to, at that distance, a 2 cent difference in price mean 41 cents overall.