How to Do Math In Your Head : Quick Math Tricks: Multiplying by 9

Uploaded by expertvillage on 22.02.2008

Hi! I'm Sean with Expert Village and I'm going to show you tips and tricks for doing math
in your head. As we've already seen, equations become much simpler when thinking of them
in terms of 10s. There's a trick that you can use when multiplying some thing by 9 to
find the answer easily. For example, if we were going to take 9x9, we can remember that
9 is the same as 10-1. You can write this equation as 9x(10-1). 9x10=90 and 9x1=9, so
it's really 90-9, a simple enough equation. 90-9=81, and that's our answer. This can also
be applied to much bigger numbers. Whenever you're doing math in your head, the most important
part is being able to visualize the numbers. The more you practice, the better you're going
to get.