Friday, October 8, 2010

A Trick For Multiplying Integers

Let a penny represent a positive number
Let a nickel represent a negative number

Thus a penny multiplied by a penny is a penny (likewise a positive times a positive is a positive)

Thus a penny multiplied by a nickel is a nickel (likewise a positive times a negative is a negative)

This little trick doesn't work with nickels multiplied by nickels


Allison said...

When I talk about multiplying and dividing integers, I tell a story about a party in math land. I use the students as examples. For instance, the seventh grade class is throwing a party, (I set up what would be an exciting/ enjoyable party for their interests) a 'positive atmosphere' and then I say, Tom is having a bad day. He is feeling negative. When Tom gets to the party he starts whinning and complaining about everything, the music, the food, the company, etc. Tom's attitude rubs off on the others at the party and so the general atmosphere becomes negative. On the other hand, when another negative student shows up, Mark, Tom now has someone to share his negative feelings with. Both Tom and Mark are now positive because they have someone to share with, and thus the general atmosthere is positive. In addition, if there are more negatives, say 3 people, and we all know three is a crowd, someone always gets left out, and so odd groups of negative makes the general atmosphere negative.
In summary, negatives in PAIRS are POSITIVE, NOT in pairs they are NEGATIVE.

Jeremiah said...

"In summary, negatives in PAIRS are POSITIVE, NOT in pairs they are NEGATIVE. "

I like that! Great idea

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