Quick Tricks for Multiplication
Why multiply?
A computer can multiply thousands of numbers in less than a second. A human is lucky to multiply two numbers in less than a minute. So we tend to have computers do our math.
But you should still know how to do math on paper, or even in your head. For one thing, you have to know a little math even to use a calculator. Besides, daily life tosses plenty of math problems your way. Do you really want to haul out Trusty Buttons every time you go shopping?
Of course, normal multiplication can get boring. Here's the secret: shortcuts. You might think of numbers as a dreary line from 0 to forever. Numbers do go on forever, but you can also think of them as cycles. Ten ones make 10. Ten tens make 100. Ten hundreds make 1000.
If numbers were just a straight highway, there'd be no shortcuts. But they're more like a winding road. If you know your way around, you can cut across the grass and save lots of time.
Multiply by 10: Just add 0
The easiest number to multiply by is 10. Just “add 0.”
3 x 10 = 30 140 x 10 = 1400
And that's the quick way to multiply by 10. Move each digit once to the left. Fill the last place with a 0.
Math: Quick Tricks for Multiplication
Name: _____________________________________________________
2 ©2005abcteach.com
Exercise A: 1. Give two reasons to get good at doing math in your head.
2. Give two situations where you might need or want to do math in your head, not with a calculator.
3. Explain the quick way to multiply by ten.
4. Solve these problems without using a calculator. a. 4 x 10
b. 15 x 10
c. 400 x 10
d. 23 x 10
e. 117 x 10
Taken from http://www.abcteach.com/free/m/mulitplication_quicktricks_elem.pdf
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