WARM UP

1) JoJo and Kiki are visiting the Empire State Building. Each of them enters a different elevator in the main lobby that can let them off on any floor from 1 to 3. Assuming that they are as likely to get off at one floor as another, what is the probability that they both get off on the same floor?

2) A family plans to have 2 children. What is the probability that both children will be girls?

3) What is the probability of getting a black jack?

HOMEWORK

4) a) 126/316

b) 5/316

c) 8/316

8) 4 drunks, 4 Jackets

10) 3 patients, 3 samples

12) 10,000 microwaves, recalled ones with last digit of 5, 6, or 7

Section 4.3Counting Rule

An easy way to find total possibilities or the

SAMPLE SPACE

Counting Rule

MULTIPLY

LICENSE PLATES

In Delaware, license plates have seven characters. How many possibilities are there total? What if you could only use numbers? What if you could only use letters? What if you can’t repeat letters? What if you do not have any

restrictions at all?

10·10·10·10·10·10·10=

10,000,000

26·26·26·26·26·26·26=

8,031,810,176

26·25·24·23·22·21·20=

3,315,312,000

36·36·36·36·36·36·36=

7.836 E 10

PASSWORDS

Most internet sites force you to have a password.

If one site requires 8 characters, letters only, how many possibilities are there?

26·26·26·26·26·26·26·26=

2.088 E 11

CELL PHONES How many phone numbers are possible

in Delaware? Are there enough possibilities if

everyone had their own cell phone? (There are about 850,000 people living in Delaware)

1·1·1·8·10·10·10·10·10·10=

8,000,000

(302)…-….

DIGITS How many five digit numbers can be

formed from the digits 2, 4, 5, 6, 7 if the number must be bigger than 50,000 without repetition?

If we allowed repetition, how many possibilities are there?

__ · __ · __ · __ · __

3·4·3·2·1= 72 ways3·5·5·5·5= 1,875 ways

__ · __ · __ · __ · __