1. What we’ve done so far…

2. If we want to put a math textbook and a math workbook in two different lockers, there are 2 ways to do it: The math textbook can go into one locker or the other, and then the math workbook can go into the remaining locker.

3. If we add a third book and a third locker, there are now more possibilities. The math textbook can go in the first, second, or third locker, leaving two books to place in the two remaining lockers. As a result, there are 6 = 3  2  1 ways to arrange the three books.

4. If we add a forth book and a forth locker, there will now be 4 places to put the new book. For each of these four possibilities, there will be six ways to arrange the remaining three books. Therefore, 24 = 4  3  2  1 ways to arrange the three books.

5. FACTORIAL

6. What is Factorial? The Factorial of a specified number refers to the product of a given series of consecutive whole numbers beginning with 1 and ending with the specified number We use the “!” to represent factorial Eg. 5! = 1  2  3  4  5 = 120

7. It’s A Fact! The number of ways of arranging n objects is n! n! = n  (n − 1)  (n − 2) ...  3  2  1

8. Calculators

9. Try these on your calculators. 6 x! = 720 9 x!  8 = 9 When do we use calculators and when is it better to do mental calculation?

10. Which is greater? 40320 8 x! 4 or x 8 65536 

11. Which is greater? 5400 5040 7 x! = 5 or x2x2  6 x3x3 =