## Monday, March 15, 2010

### Mental Math

Excel Math creates math curriculum for kids who are about 5-12 years old. We've been in this business for 30 years. One of the original features of our curriculum is called Mental Math. It's a tool for helping kids (or adults) to improve with simple math calculations. Download a copy of it if you want to have a look.

Mental Math starts out being quite easy and progressively gets harder. Each page has 12 columns of digits, separated by dotted lines. Here's how it works.

1. Choose a page from the selection of three pages.
2. Draw a line under one of the digits on the page. They are in groups that total 10, 20 and 30.
3. The example shows a red line - above it the numbers total 15.
4. You call out digits above the line, so students can add a running total in their heads.
5. When you get to the line, ask for the answer.

Note: If you chose another column, the same horizontal line will give you totals of 13, 15, 17, or 15.

Here's part of the third page, where the totals go to 100.

There's nothing magic about mental math. Except the fact that with some practice, we can do these things in our heads instantaneously.

Last week I went to the store and bought 2 items at \$1.99 each. The tax rate is 8.75%.

I knew the price would be about \$4 for the items and about \$.15 for the tax. I gave the cashier a \$5.00 bill. She handed me back \$1.84 cents. I took the change and handed back the dollar. She offered me the dollar again - I refused, saying It's not my dollar. It's yours.

She looked at the cash register. It said \$0.84 on the screen. But now she had a dollar in her hand. She looked at the dollar, at the screen, at me. She counted out \$.16 and offered it to me. I refused it.

She blushed, we all laughed and I walked away. The customer behind was getting irked...

Will the cashier be insulted if I give her a copy of mental math next time I go to the market?