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Adding and Subtracting Integers

Date: 12/31/97 at 20:07:08
From: Tracey
Subject: How to add and subtract integers

I need help on how to add and subtract integers. An example of a 
problem would be 12 + (-4) = ?. What I do is just add the problem, but 
the answer turns out to be 16. Then I would check it on my calculator 
and the answers is 8. I need help on the steps, and if you could 
explain how you did each step it would be very helpful.

Thank you.

Date: 01/09/98 at 14:33:21
From: Doctor Sonya
Subject: Re: How to add and subtract integers

I can understand your frustrations in dealing with positive and 
negative numbers.  It is a very difficult topic, but I know that you 
will get it with practice.

When I think of adding and subtracting negative numbers, I always 
imagine a number line, like this:


where each little dash stands for a number. The negative numbers are 
on the left of 0 and the positive ones are on the right. If I want to 
find 2 on the number line, I just go 2 spaces to the right. If I want 
to find -3, I go 3 spaces to the left.  

When you want to add two numbers together, think about moving on the 
number line. For example, if I wanted to find the answer to:

    3 + 5 = ?

I would first move three spaces, and them move 5 more spaces. This 
would put me 8 spaces over, and the answer to 3 + 5 is 8:

                       3  +  5  

The same principle works with negative numbers, except that you move 
to the left instead of to the right. Say you have the question:

   (-3) + (-2) = ?

To find the answer I'm going to move three spaces to the left, and 
then 2 more spaces to the left:

                -3  +  -2 

If the two numbers are of different signs, you just have to move 
different directions along the number line. Let's say I have:

   (-3) + 4 = ?

Now, the -3 means that you move three spaces to the left, and the 4 
means that you move 4 spaces to the right. Where is this going to put 
you on the number line?


Still thinking...






No answer yet...

You say that the answer is 1?  Right!  Good job.

Here are some more examples for you to practice with.

      2 + 4 =
   (-3) + 8 =
   3 + (-5) =
(-5) + (-6) =
   8 + (-5) =
      5 + 2 =
(-4) + (-3) =

Write us back if you have more questions.

-Doctor Sonya,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/   
Associated Topics:
Elementary Addition
Middle School Negative Numbers

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