Adding and Subtracting Positive and Negative Integers

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The best way to learn how to add and subtract positive and negative numbers is to look at a lot of examples.

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Here is an explanation of how to do it, though.

First of all, a positive number can be written with a plus sign in front of it, like a negative number is written with a minus sign in front. But for a positive number, the plus sign can be left off.

The absolute number of a negative number is that number without the minus sign, which is positive. The absolute value of a positive number is the same positive number.

So the absolute values of are .

You add and subtract positive and negative numbers using three basic ideas:

(1) Subtracting a negative number is the same as adding its absolute value.

For example, .

(2) If the two numbers have the same sign, add their absolute values and keep the sign.

For example, and .

(3) If the two number have different signs, either add or subtract their absolute values, keeping track of the signs using (1).

For example, .

Another example: .

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Contributed by: George Beck (March 2011)
Open content licensed under CC BY-NC-SA


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