The energy efficiency of a car is approximately 20%. If you put 10 gallons of gas into the car, how many gallons are "wasted"?

First, you find what 20% of 10 gallons of gas would be. This will show how many gallons the car actually uses.

10 gallons x 20% =

10 x 0.20 =

2 gallons used

Then you subtract that number from the total 10 gallons to get how many gallons of gas would be wasted.

10 gallons - 2 gallons =

8 gallons of gas wasted