Multiplying by the Reciprocal to Divide Two FractionsDate: 05/08/2008 at 21:38:10 From: Amanda Subject: dividing fractions I can not figure out how you divide fractions, like 2/9 by 7/45. I do not get reciprocals and how you change it from dividing to multiplying. Date: 05/09/2008 at 09:23:11 From: Doctor Ian Subject: Re: dividing fractions Hi Amanda, The "rule" is that you invert the bottom fraction and multiply by it instead. Here's an explanation of why that works: Multiplying and Dividing Fractions http://mathforum.org/library/drmath/view/58080.html A shorter explanation is that you can just use equivalent fractions to get the result. That is, if we have a fraction like 2 - 9 we can multiply it by n/n, where n is any number but zero; and we get a fraction with the same value, e.g., 2 5 10 - * - = -- 2/9 and 10/45 have the same value 9 5 45 Does that look familiar? If so, consider that we can start with this, 2 - 9 ---- 7 -- 45 and multiply both the top and bottom by 45/7, i.e., the reciprocal of the bottom fraction: 2 45 - * -- 9 7 ---------- 7 45 -- * -- 45 7 Now, what's the bottom going to equal? It has to be 1, right? So the whole thing is equal to 2 45 - * -- 9 7 ---------- 1 or just 2 45 - * -- 9 7 Which is to say, it's equal to the numerator times the reciprocal of the denominator. Does that make sense? - Doctor Ian, The Math Forum http://mathforum.org/dr.math/ Date: 05/09/2008 at 21:22:57 From: Amanda Subject: Thank you (dividing fractions) THANK YOU.....I hope my grade goes up I do understand it NOW.....THANK YOU SOOOOOOO MUCH. |
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