Friday, March 25, 2011
I really enjoy sharing little things that impress students to no end, and there are math facts you can exploit to take advantage of it, impress your students, motivate them to work hard, and work a little math practice into their day all at the same time. A quick Google search of "math tricks" is a good place to start.
Think about this: if you take any number and multiply it by nine, the sum of the digits in the answer will always be nine (provided your math is correct). Now look at it like this: no matter what digit you get students to start with, you can always get them to end up with the same number by multiplying by nine, then summing the digits. Work in a little more arithmetic just for practice, and to obscure your trick. Then tell them their answer without looking at what they've written.
Better yet, don't tell them. Show them you wrote it on the smart board before you even began!
Take a look at this notebook file. Try it out for yourself, and see if it makes sense to you. Then change the operations required to get students to practice the math skills you want them to learn.
You might just blow their minds...