Sorry Brad

Another lesson for factorials which I use is to cross out numbers... so (20! / (10! * 10!) gives

Note: I am using '.' to mean multiplication.

20.19.18.17.16.15.14.13.12.11.(10!)

----------------------------------------------- =

10.09.08.07.06.05.04.03.02.01.(10!)

Cross out 10! on top and bottom, cross out 20 on top and (4.5) on bottom, cross out 18 on top and (3.6) on bottom, cross out 14 on top and (2.7) on bottom, cross out 1 on bottom because 1 is 1. This leaves...

19.17.16.15.13.12.11

-----------------------------

10.09.08 (which is 720)

so now it's easy to grab a calculator to get the answer.

As an exercise calculate the following,

the 6/49 odds of winning are

(49! / (6! * (49-6)!)) = 13,983,816,

and Super 7 is

(47! / (7! * (47-7)!)) = 62,891,499.

Lesson concluded for today