Adding and Subtracting Integers

Date: 5/29/96 at 16:42:52
From: Jason Johnson
Subject: Adding and subtracting integers

Hello Dr.Math...

I am currently in grade 8 and I am doing adding and subtracting 
integers. I really can't grasp this concept. Could you please help 
me?

Your ever-faithful friend,

Jason Johnson

Date: 6/25/96 at 15:29:39
From: Doctor Robert
Subject: Re: Adding and subtracting integers

Dear Jason,

Probably the easiest way to 'visualize' addition and subtraction of 
integers is to use a number line.  I am sure that you are familiar 
with a number line.  If you need to add two integers you go to the 
point on the number line which represents the first number and then 
you count to the right the number of dots equal to the second number.  

It doesn't matter which number of your sum you call the first number 
and which you call the second number.  For example, suppose that you 
have to add 12 + 5.  Go to 12 on the number line and then count 5 dots 
to the right.  What number did you land on?  17!  And 17 is the sum of 
12 and 5.  You could have gone to 5 and then counted 12 dots to the 
right.  You would still land on the number 17.  

For subtraction, you must go to the first number and then move LEFT 
the number of dots corresponding to the second number.  For example, 
17 - 9.  Go to 17 and then move LEFT 9 dots.  You wind up on 8 which 
is the correct answer.

I hope that this helps.  It gets a little bit more complicated when
you have signed numbers to add and subtract.

-Doctor Robert,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/