Page 109 - Probability Demystified

98 CHAPTER 6 The Counting Rules

or

you can cancel out, as shown:

8! 8 7 6!
¼ ¼ 8 7 ¼ 56
6! 6!
You cannot divide factorials directly:
8! 40;320
6¼ 2! since 8! ¼ 40,320 and 4! ¼ 24, then ¼ 1680
4! 24

7!
EXAMPLE: Find the quotient
3!
SOLUTION:

7! 7 6 5 4 3!
¼ ¼ 7 6 5 4 ¼ 840
3! 3!

Most scientific calculators have a factorial key. It is the key with ‘‘!’’. Also
0! ¼ 1 by definition.

PRACTICE

Find the value of each

1. 2!
2. 7!
3. 9!
4. 4!
5. 6! 3!
6. 4! 8!
7. 7! 2!
10!
8.
8!
5!
9.
2!
6!
10.
3!