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Working with Integers August 28, 2009

Posted by Ms. Miller in Algebra I.
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When you add or subtract integers (positive and negative numbers), keep the following in mind:

If the signs are the SAME Add the numbers and keep the sign. Ex. 7+2=9 and -3-7=-10
If the signs are DIFFERENT Subtract the smaller number from the larger. The answer takes the sign of the larger number. Ex. (-8)+5=-3 and 9+(-2)=7

Here’s a story that may help you remember what to do when multiplying or dividing positive and negative numbers:

In an Old West town, there are good guys (positive) and bad guys (negative) who are entering (positive) or leaving (negative) the town:

If the good guys (+) enter (+) the town, that is good (+) for the town. (+)(+)=+
If the good guys (+) leave (-) the town, that is bad (-) for the town. (+)(-)= -
If the bad guys (-) enter (+) the town, that is bad (-) for the town. (-)(+)= -
If the bad guys (-) leave (-) the town, that is good (+) for the town. (-)(-)=-
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