Randy can buy 6 gallons of gas for $18 or 7 gallons of gas for $21. how much do you think he would pay for 8 gallons of gas? a) $22 b) $23 c) $24 d) $25

Well, we want to find how much it would cost for 1 gallon, the easiest way to do that is subtract 21 from 18.

21 - 18 = 3

So, it's 3 dollars per gallon. Now that we know that we multiply it by 8 to find how much it would cost.

8 x 3 = 24

Eight gallons of gas would cost 24$ :D

There are several ways to solve this. First, you can divide $18 by 6, which is $3, to find the price for one gallon, then multiply this by 8 (so the total would be $24).
Or, you can use this less conventional and more complicated method to try to impress your teachers with how smart you are: Multiply the price for 6 gallons by 4, to find the price for 24 gallons ($18*4=$72), then divide it by 3 (since 8*3=24) to find the price for 8 gallons. This is $72/3=$24.