Q&A #286

Teachers' Lounge Discussion: Teaching conversion of units of measurement

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From: Kari O'Connell

To: Teacher2Teacher Public Discussion
Date: 1999020219:40:31
Subject: unit conversions ideas

I am just starting a geometry unit on area and perimeter, and I insist upon showing all units. I found students often ask whether to multiply or divide. So now I tell them to ALWAYS multiply by "1", but they have to figure out the correct form of "1". For example, since 1 foot = 12 inches, I could write the number 1 as 12inches / 1 foot or I could write it as 1 foot / 12 inches. I choose, by picking the one where the units I WANT are in the numerator. That way the units I am converting from, cancel out. My success is based on the assumption that in the previous algebra course, students have muliplied a x (b/a) ex: convert 44 inches to feet: 48 in x 1 ft = 4 ft ------ 12 in ex: convert 20 feet to inches: 20 ft x 12 in = 240 ft ------ 1 ft

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