



What if
I said:



"I'm
thinking of a number, and if you add 2 to it 


you get
5. 


What
number am I thinking of?" 





Well that
one's not too hard. 


We know
that: 





3 + 2 = 5 





So the
number I was thinking of was 3. 





Math
people are always asking questions like that 


(Hey,
that's what they do!) 


So they
wanted to come up with a quicker way 


of saying
stuff like: 


"I'm
thinking of a number. If you subtract 4 from it 


you get
2. What number am I thinking of?" 





At first,
they got the bright idea to write: 





?  4 = 2 





And then ask:
What's the "?" 





This particular
"?" is 6, because 6  4 = 2 





Using a
"?" for the number you were looking for 


worked
fine for easy problems, 


but later
harder problems they ran into troubles. 


So they
decided that instead of a "?" they'd use an "X". 





So stuff
like: 


?  4 = 2 





was now
written as: 


X  4 = 2 





BUT IT
STILL MEANS EXACTLY THE SAME THING. 





OK, 


I'm
thinking of a number that if you add 2 to it, you get 6. 


What
number am I thinking of? 





With a
problem like this, 


we can
probably just look at it or count on our fingers 


and say: 





If
X + 2 = 6 then X = 4 





Because
4 + 2 = 6 





But as
the problems get more complex, 


we start
needing another way to get the answer. 





To deal
with hard problems, 


we have a
set of rules we can use 


to find
the thing we don't know (X). 





So start
with a problem like: 





X  4 = 2 





and we
want to wind up with: 





X = (something) 





with the
X all by itself, 





The first
trick to help us do this says: 











So here,
that means we add a 4 to each side 


to
"get rid of" the  4 next to the X 











Let's
try a few more: 





Examples: 











copyright 2005 Bruce Kirkpatrick 
