Answer: 20 miles per gallon.
Step-by-step explanation: All you simply need to do is to find how many miles is 1 gallon of gas.
Step 1: Divide 5 gallons by 5 5 divided by 5 = 1 gallon of gas
Step 2: Divide 100 miles by 5 100 divided by 5 = 20 miles
Step 3: 1 gallon equals 20 miles.
So, for every 1 gallon of gas, you will travel 20 miles.