BodhiAI

Nov. 15, 2019

**Factorial Notation**

**The product of first n natural numbers can be written as (n)!**

** (n)! = n(n-1) (n-2) .............3.2.1**

**thus; (n)! = n(n-1)! = n(n-1) (n-2)!**

**also; (0)! = 1**

**Fundamental Rule of Association**

**A. Sum Rule**

**Suppose A can occur in m ways and B can occur in n ways and both cannot occur simultaneously. Then A or B (at least one of them) can occur in (m+n) ways. This rule is also applicable for two or more exclusive events.**

**B. Product Rule **

**If there are m ways of doing a thing and when it has been done in any one of these m ways, then there are n ways of doing a second thing, then the total number of ways of doing two things together are m×n. **