Tuesday, December 22, 2009

Division of Fractions with Common Denominators

We teach division of fractions using common denominators. The kids have picked up on this easily, but for some reason don't want to change the numerators when they find the common denominator. The don't do this when they add or subtract, just divide. Any ideas on how to remind them to change the numerator as well as the denominator when they are dividing?
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2 comments:

  1. PJ DavisJanuary 3, 2010 at 3:47 PM

    Another math teacher on my grade level uses a grid chart. She stacks the two fractions on top of each other and continues the fraction bars out and makes a chart with 5 columns. Using the denominators - she multiplies out across the columns (x's 2, x's 3, x's 4, x's 5) Once they find the common denomiator, they multiply the numerators only in that colums - if they do not multiply they cannot find the equivalent fractions with the LCD. I will try to get a copy of the process worked out - I know the description is a little confusing.

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  2. AlmarieMarch 21, 2010 at 2:33 PM

    This is the way we teach division of fractions too. My students do it well because of addition and subtraction of fractions. The only problem I find is that the students want to find the LCM/LCD for multiplication of fractions. They figure, if you find LCM/LCD for addition, subtraction, and division, why not use it for multiplication. We have since corrected that problem. Eventually your students will start changing the numerator, they just have to continue repeating the process.

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