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couple of questions
Old 01-09-2006, 08:29 PM
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First of all, what grade do you teach? (I teach 5th/6th Math & Science.) Second, I can't for the life of me figure out how you could cross multiply to compare fractions. Can you explain that a little more?

Personally, I hate teaching LCM and GCF. I tell my kids that they need to know what those mean and how to find them because they will be tested on it on standardized tests, but that in reality, it really doesn't matter if you find the LCM for a common denominator or the GCF to reduce a fraction as long as find *something* that works. The worst that can happen is that you end up with fractions with big numbers (using the LCD obviously gives you the smallest numbers to work with) or that you may have to simplify more than once at the end. So what? I tell my kids (maybe I'm wrong - maybe I'm not being a good math teacher here - ?) to just figure out any denominator that works for the two fraction and make equivalents, and then to just check their answers to make sure they are completely simplified - and if not, simplify again. (I'm thinking about adding fractions here - not just comparing.) I don't know - maybe my way sounds like more work, but who wants to sit there and write out all the factors/multiples of a pair of numbers just to find the "right" one? My kids sure don't - and neither do I.

Anyway, sorry for rambling - I've had a really long day and am running on very few hours of sleep. : )
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