Multiplication trick

If you enjoy math 'tricks', here's one presented nicely in a slide show:


How to multiply numbers with 11-19 in less than 5 seconds


It explains how to multiply by 11, 12, etc.

And... here's a challenge (you can ask this of students, too):
After watching the slideshow, explain how it actually has very similar things going on as the standard algorithm.

In other words, how do the standard multiplication algorithm (in columns) and this one compare?

Comments

Anonymous said…
Check this out for fast multiplication of 2-digit and 3-digit numbers

http://www.metacafe.com/watch/315070/cool_mathtrick_really_fast_multiplication/
Maria Miller said…
Yep, that's a nice, short, and very well done video explaining a 'shorcut' way of multiplying.

Here's the link again so you can click on it:

Fast multiplication of 2-digit and 3-digit numbers (video)

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