The Math Forum

Ask Dr. Math - Questions and Answers from our Archives
Associated Topics || Dr. Math Home || Search Dr. Math

Dividing Fractions

Date: 8/4/96 at 16:1:48
From: Jeffrey Paul Goins
Subject: Dividing fractions

Dear Dr. Math,

Why do you flip the second fraction when dividing fractions (who 
figured that out anyway)?  

Thank you!

Levi Goins

Date: 8/5/96 at 11:29:51
From: Doctor Anthony
Subject: Re: Dividing fractions

Why when dividing fractions do you turn the second one upside down and 
Example 5/(1/2) = 5*2 = 10

By keeping the rules consistent this rule is easy to derive.

A fraction is unchanged if you multiply top and bottom by the same 
number. In this case if we multiply top and bottom by 2 (which is 1/2 
turned upside down) we get:

   (5*2)/{(1/2)*2} = 10/1 = 10

You will notice that by multiplying top and bottom by the bottom 
fraction turned upside down we are ensuring that the denominator of 
the original fraction becomes equal to 1.  In practice this is 
achieved by applying the rule you quoted.

-Doctor Anthony,  The Math Forum
 Check out our web site!   
Associated Topics:
Middle School Fractions

Search the Dr. Math Library:

Find items containing (put spaces between keywords):
Click only once for faster results:

[ Choose "whole words" when searching for a word like age.]

all keywords, in any order at least one, that exact phrase
parts of words whole words

Submit your own question to Dr. Math

[Privacy Policy] [Terms of Use]

Math Forum Home || Math Library || Quick Reference || Math Forum Search

Ask Dr. MathTM
© 1994- The Math Forum at NCTM. All rights reserved.