Estimating Fractions/Mixed Numbers

Date: 01/10/2002 at 20:06:38
From: Lynn
Subject: Estimating fractions/mixed numbers

Hello, 

I need your help. I don't understand how to estimate fractions.  

Example: I am to find an estimated sum of 1/6 + 5/8, or 13 1/8 divided 
by 6 1/5.

Please explain how I estimate an answer for these problems. Is there a 
formula?

Date: 01/10/2002 at 23:11:11
From: Doctor Peterson
Subject: Re: Estimating fractions/mixed numbers

Hi, Lynn.

There can't be a "formula" for an estimate, since an estimate is by 
definition a deliberately wrong answer. You have to decide for 
yourself how accurate you want to be, and then decide based on the 
circumstances what it takes to get that level of accuracy as easily as 
possible. Perhaps you are being taught some techniques, but in the 
long run there is no right and wrong here.

For your first problem, I would probably say that 1/6 is a bit bigger 
than 1/8, so the sum will be a bit more than 1/8 + 5/8 = 6/8 = 3/4.

For the second, I would just drop the fractional parts, which don't 
make much difference, and divide 13 by 6. Then I'd simplify that and 
just call it 2. If I needed a closer estimate, I'd get a calculator!

Mostly, estimation depends on familiarity with how numbers work, so 
you can judge what changes you can make that will not affect the 
answer much. One way to build that familiarity is to make a lot of 
estimates as well as you can (avoiding as much actual calculation as 
possible), and then compare with the actual answers. When you find you 
were far off, take a moment to ask yourself what went wrong, and what 
you could do to adjust your estimate. No "formula" can take the place 
of that sort of experience.

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