Lesson 2 — Activity 2: Adding Integers



Getting Ready


The addition of integers can be done in a variety of ways, such as using a number line or a calculator.

In this activity, you will learn how to add positive and negative integers.

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When dealing with integers, it is important to remember the following rules:


Rule #1: Adding two positive integers always gives you a positive integer for an answer.

Rule #2: Adding two negative integers always gives you a negative integer for an answer.

Rule #3: The sum of any integer and its opposite is equal to zero.

Rule #4: To find the sum of a positive and a negative integer, take the absolute value of each integer and then subtract these values.


We can use a number line to show how these rules work.

Rule #1:

Positive + Positive = Positive

2 + 3 = 5

Look at the number line below. If we start at +2 and move 3 to the right (the positive numbers), we land on +5.



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Click here for an interactive activity where you will practice adding positive integers on a thermometer.


Rule #2:

Negative + Negative = Negative

–2 + –3 = –5

Look at the number line again. This time, if we start at –2 and move 3 to the left (the negative numbers), we land on –5.

Click here for an interactive activity where you will practice adding negative integers on a thermometer.


Rule #3:

Any integer plus its opposite integer is equal to zero.

*Note: Two integers that are the same distance from the origin (zero) but are on different sides of the zero are known as opposites. For example, –4 and +4 are opposites. Therefore, when you add an integer plus its opposite, the sum is equal to zero.


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Rule #4:


To find the sum of a positive integer and a negative integer, take the absolute value of each integer and then subtract these values.


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Follow these steps to find the sum of a positive and negative integer using a number line:




Here is one more way that might help you remember how to add integers:


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Now let's apply this rule to our thermometer. If the temperature is –2 (just a little chilly), and we know from the radio that it is going to drop by another 6 degrees by dinnertime, then we are using this equation:

–2 degrees in the morning (dropping by 6 degrees) by dinner means it will be –8 degrees by dinnertime.

The equation looks like this:

–2 + (–6) = –8


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Hint: Do not confuse the sign of the integer with the operation being performed. In this case, the sign of the integers is the negative sign (–), and the operation being performed is addition (+). Sometimes, as in the example above, you will see parentheses (or brackets) used around integers and their positive and negative signs to make things less confusing when doing mathematical operations.

    Remember that –2 + (–6) = –8.

    This equation is read as:


    "Negative 2 plus negative 6 equals negative 9."

  Self-check!

Try this!


Try this activity where you will practice adding and subtraction integers. Answer these questions on your own first. When you are finished, click on the tabs below to check your answers.


You have heard on the radio that the current temperature of 12 degrees will rise 10 degrees by this afternoon. What temperature will it be in the afternoon?


You have heard on the radio that the current temperature of 12 degrees will drop by 15 degrees by the afternoon. What temperature will it be in the afternoon?


Your town's website states that the temperature will drop by 20 degrees overnight. Right now it is -5 degrees. What will the overnight low be?


Today's temperature is 30 degrees. Last year on the same date the temperature was only 15 degrees. What is the difference in temperature between today and last year?

The difference was a decrease by 15 degrees


The morning news states that today will be -18 degrees. Friday it will be -28 degrees. How many degrees will the temperature drop by Friday?

It will drop by 10 degrees


Digging Deeper

Click here to download a document that will show you how to add integers using a calculator.


Click on the Play button below to watch a video on how to add positive and negative integers.