Factorial

Date: 4/1/96 at 7:14:46
From: Leigh Ausband
Subject: Factorial

From Mrs. Fields' seventh grade math classes at 
Robert Smalls Middle School, Beaufort, SC.

Dear Dr. Math,

What is factorial?  For example: 4 factorial.  What is it used for?

Eric Peevey

Date: 4/2/96 at 4:2:32
From: Doctor Jodi
Subject: Re: Factorial

Hi Eric!

4 factorial is written 4! and means 4*3*2*1
 
Say you were having a lottery and were picking 4 numbers out of 60 with 
no repeats of numbers.

You'd find out the probability of picking a certain 4-number set (in a 
certain order) by saying

60 choices for the first number, 
59 for the second, 
58 for the third, 
57 for the fourth.

So there are 60*59*58*57 ordered sets of 4 numbers.

This can also be written as

60!
---
(60-4)!

which will give you 60! divided by 56!

Since the numbers 56 and less divide out, you're left with 60*59*58*57 
as the number of ordered sets of 4 lottery numbers that could be drawn

-Doctor Jodi,  The Math Forum
 Check out our web site!  http://mathforum.org/dr.math/