Multiplying two digit numbers!

Hey guys, this is a continuation of my last post :).

So you've figured out how to square any value with the formula I gave out, but what about two multiplying two different numbers? Well, its simple, but a little more complicated.

So, lets use an example: 27*46.

Let's break this problem up.

We know that 27 = 20 + 7 and 46 = 40 + 6

so (20+7)*(40+6) = 27*46.

If we set a = 20, b = 40, c = 7, and d = 6, we get:

(a+c)*(b+d)
= ab + ad + cb + cd

27*46 therefore is:

(20)*(40) + (20)*(6) + (7)*(40) + (7)*(6)
= 800 + 120 + 280 + 42
= 1242

Amazing!

So remember, its the two big numbers multiplied, plus one big times one small, plus the other big times other small, and the two small multiplied which makes sense!