Solving Problems Without Paper

Date: 9/1/95 at 19:9:51
From: Megan Lee Mead
Subject: working problems in my head

	My name is Megan Mead.  I'm in seventh grade and I'm having trouble 
when we have to do problems in our head instead of on paper.  Do you have 
some ideas on what will help me?

Date: 9/2/95 at 11:47:11
From: Doctor Ken
Subject: Re: working problems in my head

Hello!

To tell you the truth, I'm actually not all that good at doing numbers in my 
head either.  I have gotten better at it though, and here's what has helped 
me.  

I don't try to do the addition and multiplication the way that people learn 
in school, starting on the right and working toward the left. I actually 
start on the left and go right.  I find it easier because you don't have to 
remember the numbers in the reverse order you really want them in.  For 
example, if we had 342 + 831, here would be my steps:

  342
 +831
 ----
 11

  342
 +831
 ----
 117

  342
 +831
 ----
 1173

The only weird part is when you have to carry numbers.  Then you have to go 
back and change what you had before:

  746
 +487
 ----
 11

  746
 +487
 ----
 122

  746
 +487
 ----
 1233

I do the same thing for multiplication, but that gets a little more tricky 
to remember all the steps.  Can you figure out how to do that?

-Doctor Ken,  The Geometry Forum