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Comparing Fractions: LCM or Cross Multiply
Old 01-09-2006, 04:39 PM
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I'm new to teaching math and I am currently in our chapter on factors and fractions. We have completed the lessons on GCF and LCM and today I gave a lesson on comparing fractions by writing equivalent with an LCD.
A few students asked if they could just cross multiply bc it was a lot easier.
My take on it was that, the concepts I was teaching was different. I gave students strategies to use when one or both denominators were prime and when one denom. is a factor of the other.
What do you suggest? Should I teach to the easy/fast method or teach the LCM=LCD method instead? Or just offer it as another method they an use. But then, do I mark them off on a test/quiz for doing the fast method since it isn't what we took notes on?

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