## Add and subtract decimals by lining up the decimal points.

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Guzzling Gasoline

Credit: Daniel Oines
Source: http://www.flickr.com/photos/dno1967b/5642103644/

Have you ever been to the gas station with your mom or dad to fill up the car? If you have, you've probably spent part of the wait watching the numbers climb on the screen at the pump. Those screens display how much you have spent based on the cost per gallon and the number of gallons you've added to your car's gas tank. With this in mind, think about where you can find decimals at the gas station.

#### Why It Matters

Gas stations usually sell different types of fuel that each cost different amounts per gallon. The first place you'll see decimals at a gas station is wherever the prices per gallon are displayed—the most obvious location is the big sign out in front of the station. Another decimal is the total amount of money you spend after filling up the car. You can see that figure on the screen at the pump and at the bottom of your receipt. But there is one more decimal you can see—and this is where addition comes in!

Credit: Nate Grigg
Source: http://www.flickr.com/photos/nateone/2872138492/

Take a look at the numbers displayed on the screen of the gasoline pump pictured above. The number of gallons are actually calculated in parts per thousand. The value to the left of the decimal gives us the whole number of gallons you have bought with the money you have spent. The values to the right of the decimal point give us the measure for tenths of a gallon, hundredths of a gallon, and thousandths of a gallon.

As each part of a gallon is added to the previous parts of the gallon, the parts per gallon continue to increase until another whole gallon is added. Adding parts of decimals to parts of decimals results in whole gallons of gasoline. Notice that the customer of the pump pictured above received a total of 1 and 765 thousandths of a gallon.

#### Explore More

Visit the first link below to test your decimal addition skills in a game of "soccer math." Check out the next website to practice adding and subtracting decimals at "Hotel Decimalfornia."

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