# Neat trick for multiplying/dividing integers

Discussion in 'Sixth Grade' started by Teacheroo, Sep 9, 2007.

1. ### TeacherooCompanion

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Sep 9, 2007

I just learned this trick and thought I'd share it. I had tons of light bulb moments in my class when I shared it with them! Hopefuly it makes sense on here.

Good Guy (+) Comes to town (+) Good thing (+)
____________ _______________ _______________

+ x + = +

- x + = -

+ x - = -

- x - = +

So...If a good guy comes to your town it's a good thing (+)
If a good guy leaves your town it's a bad thing (-)
If a bad guy leaves your town it's a good thing (+)

A little easier for my kids than just memorizing the rules.

ETA. Well, this didn't work like I meant for it to. I couldn't get my +/- to line up under the columns. if you have questions about it just ask.

3. ### JaimeMarieModerator

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Sep 9, 2007

That is way confusing for me. Sorry.

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Sep 9, 2007

It is about multiplication with signs. It is a way to remember that a negative times a negative is a positive, and that a negative times a positive is a negative (and so on). I think it is pretty straight forward. Stories help people learn and remember. Nice idea.

5. ### smalltowngalMultitudinous

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Sep 9, 2007

I get the story aspect of it, but in your first explanation you said a bad guy leaves your town its a bad thing (-x-=-) but then in the story you said if a bad guy leaves your town its a good thing (-x-=+)

6. ### JaimeMarieModerator

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Sep 9, 2007

That is why I was confused too.

And what happens when you have a bad guy times a bad guy? that is a postive?

7. ### AliceaccMultitudinous

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Sep 9, 2007

I told a version of that to my 9th graders on Friday. Only in the version I've heard it's "when a bad thing happens to a bad person..." Certainly not a philosophy to live by, but the kids find it cute:

When a good thing happens to a good person, that's good.

Disclaimer: this is not my philosophy, nor is it the one my school espouses. But it's a cutesy thing to show them.

8. ### jarubyCompanion

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Sep 9, 2007

Its supposed to be a table and the x and = sign on the top are just seperating the rows, it is not an equation. Her formatting is off so it smushed everything together.

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Sep 9, 2007

WOW! i teach second grade but this makes great sense to me!! Too bad I won't need to use it this year!

10. ### lupin43Companion

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Sep 10, 2007

I use a similar analogy. Tigers and Bears. Both are the same strength so if put in the same cage - they both die.

bears(+) + bears = more bears (add, pos.)
tigers(-) + tigers = more tigers (add, neg.)
tigers + beats = who wins, by how many (subtract, use sign of large values)

Subtraction is hard to explain with just words, but it boils down to adding the opposite.

Multiplication

groups of animals.

4*3 (4 groups of 3 bears) = 12
4 * (-3) (4 groups of 3 tigers) = -12
-4 *-3 (TAKE OUT 4 groups of 3 tigers, leaves bears) = 12
-4 * 3 (take out 4 groups of 3 bears, leaves tigers) = -12

The kids really get into the idea of dead animals all over the place. Is it PC, probably not, but they certainly remember it.

***Disclaimer****
No animals were harmed in the creation of this post or in the implementation of this lesson plan.

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Sep 10, 2007

Isn't it easier just to remember, 'sign's the same, answer is positive'?

12. ### smalltowngalMultitudinous

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Sep 10, 2007

That's great Upsadaisy!! I never could really remember signs...of course, I'm sure it would have been easier had I been told this.

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Sep 10, 2007

Remember, that's only when multiplying and dividing, though. When we work on integers, I repeat these rules soooooo many times that they become like a mantra!

14. ### MrsCMultitudinous

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Sep 11, 2007

That's what I do!

15. ### TeacherooCompanion

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Sep 12, 2007

yeah, sorry everyone. It was supposed to be a table. The top part was supposed to be column headings.
Basically its this:

If a good guy (+) comes to your town(+) its a good thing (+)