Fundamental counting principle  Permutations and Combinations
Fundamental counting principle
The fundamental counting principle can be very helpful when you need to figure out the possible number of outcomes of multiple events. The principle essentially works like this: If there are m possible ways for an event to occur, and n possible ways for another event to occur, there are m x n possible ways for both events to occur. In this lesson, we will apply the principle to reallife scenarios to see how it works.
Lessons

4.
Fundamental Counting Principle Involving Restrictions – "restriction must be dealt with first!"
How many odd four digit numbers are there?
An example of a four digit number is 3581, while 0492 is a three digit number. 
5.
Use only the digits 2, 4, 5, 6, 7, 8 and 9 to produce four digit numbers.