Front End Estimation of Addition Problems

Date: 09/06/2005 at 19:53:51
From: Kristin
Subject: front end estimation

Could you give me an example problem so I can learn how to do front 
end estimation?  Here's an example:

  436     400
+ 517   + 500
_____________    
          900

Is this correct?

Date: 09/06/2005 at 22:59:14
From: Doctor Peterson
Subject: Re: front end estimation

Hi, Kristin.

Yes, that's correct.

The main idea of FEE is that the "front-end" digits (the ones on the
left) are the most important because their place value is the 
greatest.  So if you want to estimate by ignoring most digits and
using as few as possible, you will do best if you use only the "front
end", and replace everything else by zero, as you did.

There are other tricks for getting a better estimate which you will be
learning later--these may be called "adjustments", or may be taught as 
"rounding".  What you've learned should be enough for the moment, but 
you will do well by thinking after doing each problem, "How far off do 
I expect my answer to be?  Will the exact answer be more or less than 
what I estimated?" 

Then do the exact addition and see if you were right.  Do that enough,
and you'll be a good estimator!

So make up your own problems, and then check your answers that way. 
That will be worth more than any sample problems I could give you. 
You may run across some tricky cases; if you don't understand why some
of your estimates are farther off than you expected, write back and
tell me what you found, and we can discuss it.


- Doctor Peterson, The Math Forum
  http://mathforum.org/dr.math/