Two Ways to Solve an Equation

Date: 1/23/96 at 21:28:24
From: Anonymous
Subject: MATH

X + 3 = 7

Date: 3/4/96 at 22:46:2
From: Doctor Jodi
Subject: Re: MATH

Hi there!  

I can think of two ways to solve the problem you sent us - x + 3 = 7

One way is to think about what number, added with 3, will give you 7.  
I can make a guess and then check my answer.  If I guess 5, I find out 
that 5 + 3 = 8, so that can't be the answer.  Then I try 4, and check to 
see: 4 + 3 = 7, yes, 4 is the answer.

The other way uses the idea that addition and subtraction are opposites. 
Does that make sense?  If I add 5 to 3, I get 8.  I can get 3 back by 
subtracting the same number I added: 8 - 5 = 3

So if I take your equation, x + 3 = 7, and subtract 3 from each side, 
I get:

x + 3 = 7

-3      -3
___________

x = 4

Does this make sense?  Write back if you have more questions.

-Doctor Jodi,  The Math Forum