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Q&A #1493

Teachers' Lounge Discussion: Dividing fractions

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From: Loyd <Loydlin@aol.com>
To: Teacher2Teacher Public Discussion
Date: 2010100311:31:47
Subject: Re: Re: why

My last was too wordy.

So, why do we invert:  

I can't make the divide symbol, so I will just use div. 

3          2
--   div   -- ( 3/4 is a numerator and 2/5 is a denominator)
4          5

The denominator is also called the divisor.

Next multiply the numerator and divisor by the same thing. That is,
the reciprocal of 2/5 or 5/2.  

3    5           2    5       15            15
-- x --   div   --  x --  =  ----  div  1 = ----- 
4    2           5    2        8             8

So, you see it easier just to say, invert the divisor and multiply
because it is the same thing.  1 is the identity element for
multiplication and division, so we can ignore that. 


As I said in the previous post, the divide symbol almost disappears by
the time you get to algebra. 

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