Signed numbers include integers and other rational numbers that have either a positive or a negative sign.

Source: Badwater Elevation Sign, Complex01 and Elevation Benchmark, Jeff Kramer, Wikimedia Commons

The sign of a number can be used to indicate a direction from a reference point, such as an elevation above or below mean sea level.

The sign of a number can also indicate a gain or a loss, such as a change in value of an asset, for example a share of stock in a corporation.

Use the diagram below to review standard procedures for adding, subtracting, multiplying, and dividing integers. Click on the operation symbol to see more details.

Practice

1. Mrs. Broussard spent $145 at the department store on clothing, and she used her credit card for her purchases. As a result, the balance on her next credit card statement was −$145. She paid $55 of her bill right away, and then she paid $40 of her bill a few days later. After the two payments, what was the balance on Mrs. Broussard’s credit card?

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   Since the balance is shown as a negative number, each payment is a positive number that cancels out a portion of the balance.
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   Check Your Answer

   −$145 + $55 + $40 = −$50
   
   Mrs. Broussard will have a −$50 balance remaining on her credit card, meaning that she will still owe $50.
2. One winter morning, the temperature in Amarillo, Texas, was −15°C. That same morning, the temperature in McAllen, Texas, was 12°C. What was the difference in temperature between Amarillo and McAllen?

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   Use the following number line to represent −15 and 12:
   
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   12 – (-15) = 12 + 15 = 27
   
   The difference in temperature was 27°C.
3. At the end of the day, the newspaper reported the change in stock price for one share of stock in Computers Corporation to be −$2. Meredith owns 45 shares of stock in Computers Corporation. What was the change in the total value of the stock Meredith owns?

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   What does a change in price of −$2 represent?
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   Check Your Answer

   −$2 × 45 = −$90
   
   Meredith’s stock changed in value by −$90.