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Volume 2 • #3 • November 2002


Now that Hallowe’en is past, it is time to ditch the disguises and expose the real thing underneath. In the last newsletter about fractions, I put a disguise on a fraction to make it look fatter by multiplying both top and bottom by the same number, which, as you all know, is a disguised 1. Taking the disguise off is easy if you were the one who put it on in the first place. You know which fraction with the matching top and bottom you multiplied by, so all you have to do is to divide the top and bottom by it. But if someone gives you some overstuffed fraction, like, say, 108 over 270 and you started taking out two over two, you still have to take out nine over nine, and you STILL have to take out three over three. Obviously the fatter the disguised one you can take off, the sooner you are finished. (Those math teachers with bad consciences about using anything but correct terms can say you go for the greatest common multiple.)

Some years ago when I was teaching a seventh grade math class, the educational buzz words were “making education relevant” and “getting parents involved in their children’s education”. We had been monkeying around with fractions and proportions just before Thanksgiving and I had what I thought was a brainstorm. I said to the kids that if they had eight or ten people for Thanksgiving dinner, how did they think their Mom figured out how big a turkey to get, or how much pumpkin pie she would need for that many people? I suggested that they ask at home, thinking that this was a way to have Mom look brilliant and the kid realize why we did all this stuff in class.

A few of them actually asked, and the answers all came back the same:

“Good heavens, I don’t go through all that. I just guess!”

So you know who the turkey was that time. On the other hand, it reinforces my contention that most of what any ordinary mortal does with math is estimate, and if you don’t know the times table FAST and basic information about percentages and probability, you may lose a lot of money on lottery tickets and interest charges on your VISA card. You can safely ask anybody how to spell antibody or especially, but if you ask how much 9 x 7 is, they look at you funny.

Teaching tip:

Whenever you call on somebody in class there are always a few kids who promptly go to sleep because they feel safe for the moment. To keep everybody paying attention, try this: have a small pile of papers and a magic marker at each desk. When you ask a question, have everybody write the answer on the paper with the magic marker and hold it up toward you for you to see. This works well for arithmetic, spelling, etc, where there is apt to be one answer. Not only does everybody get “called on” at once, but you can see at a glance what sort of mistakes some kids are making. (Be sure that when the bell rings, each kid replaces the magic marker on the desk before he tears out the door!)



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