No, the above presentation isn't technically a video. It's a presentation from SlideShare. What YouTube is to videos, SlideShare is to PowerPoint and OpenOffice presentations. Yes, Mac users can create presentations as well, using Keynote, or the Mac versions of the above packages.

This particular presentation teaches you how to square numbers ending in 5 in your head, and then how to use the same technique to mentally multiply numbers that are equidistant from the multiples of 5. To step through the presentation, simply use the two middle arrow keys to step back and forth through the presentation at your own pace.

If you like this mental math technique, you can also learn to do instant subtraction, multiply by 11 through 19, and divide by 9 in your head, too!

Video Format:
SlideShare