This week's newsletter is also available in Spanish, thanks to Ed Campos, Jr. Make sure you tell him thanks and share the link with friends: bit.ly/TTMspanish40
Math tends to come with some shortcuts, easy ways to remember things, or "tricks" to abide by. This week, I brought in Tina Cardone, author of Nix The Tricks and all-around amazing person, to share her thoughts on the matter:
Have you seen people using their fingers to multiply by nine? There’s this trick where if you put down the finger corresponding to the other factor, you can read the product off your remaining fingers. Fingers to the left represent the tens place digit and fingers to the right represent the ones place digit.
If you or your child haven’t seen this trick before take some time to play and verify that it really works. Then ask kids’ favorite question - why?
Ask your child to do some observing and look for reasons behind the patterns. It might help to write down the numbers to be able to see a pattern.
9 * 1 = 9
9 * 2 = 18
9 * 3 = 27
9 * 4 = 36
9 * 5 = 45
9 * 6 = 54
9 * 7 = 63
9 * 8 = 72
9 * 9 = 81
9 * 10 = 90
The big idea here is that we have ten fingers and a base ten number system (every time you count to ten you start over in the ones place). Using the idea of "nine is one less ten" we can figure out that every multiple of nine will be that many less than the decade number (multiple of ten).
For example: 10 x 3 = 30 so 9 x 3 = 30 - 3 = 20 + 7
Putting down your third finger leaves two fingers to the left (twenty is the decade number less than thirty) and 10 - 3 fingers to the right (you have ten fingers! Your fingers show you the seven.)
Try it out for some other multiples of 9. Get it now?
Every time I see a math trick, first I verify that it really works and then I ask why. Asking “why?” is what math is all about! Once you’ve figured out the reasons behind a trick, you can rename it a strategy. There are lots of tricks that people use in math class without understanding the math - so many that I wrote a book about them called Nix the Tricks. If you’re interested in turning more tricks into strategies, check out the free download.