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### Understanding Negative Numbers

```
Date: 5/18/96 at 17:8:37
From: Anonymous
Subject: negative numbers

I don't understand negatives - can you help me?
```

```
Date: 7/19/96 at 19:51:25
From: Doctor Jodi
Subject: Re: negative numbers

Hi there! Did you want information on adding and subtracting or
subtraction.  If you need more help, please write us back.

Subtracting a number from a negative number is like starting below
zero on a thermometer and removing more heat. Sounds wierd but if the
temperature is -13, not only is it cold, but it is BELOW ZERO.  If we
remove 6 more degrees of heat, it gets colder and the mercury moves
down the scale 6 more degrees to -19.  Make sense? So subtracting a
number is like moving down the thermometer.

The other part of your question is trickier.  Subtracting a NEGATIVE
number is like REMOVING a debt.  Let's think in terms of money.  If I
owe you 5 dollars, it could be written as -5 in my book, to remind me
that I must remove 5 dollars from my account.  But if you say "Oh
forget it. You don't owe me any more," then I need to subtract the
debt from my books. It's like saying -(-5), which to ME is like adding
the money back into my account.  What we say is that subtracting a
negative is JUST LIKE adding a positive.  So  let's get specific.

If I SUBTRACT -5 from 12, I can write it as 12-(-5) which is JUST LIKE
12 + 5 which is 17.

You might also want to think about how we can show this on a number
line. A thermometer is a vertical number line.  Discuss this with your
teacher and other students.  If you want to get back in touch with us,

-Doctor Chaos and Dr. Jodi, The Math Forum
Check out our web site!  http://mathforum.org/dr.math/
```
Associated Topics:
Middle School Negative Numbers

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