# Suppose a fuel mixture is 5% ethanol and 95% gasoline. How much ethanol (in gallons) must you add to one gallon of the fuel so that the new fuel mixture is 10% ethanol?

##### 1 Answer

You need to add **0.0556 gallons** of ethanol to the mixture.

#### Explanation:

You know that your mixture is **5%** ethanol and **95%** gasoline.

To determine how much ethanol you need to add to the 1-gallon sample in order to get the percent concetration of ethanol in the mixture to **10%**, you first need to determine how much ethanol your sample currently has.

For a 1-gallon sample, you know that

Let's say that *new percent concentration* of ethanol like this

This is equivalent to

So, if you add **0.0556 gallons** of ethanol to the 1-gallon sample, you'll get a total mixture of **1.0556 gallons** that is 10% ethanol.