Download Probability

Probability
Probability
If I do this then what?
 Probability looks at chances of an
outcome
 A measure of how likely it is that some
event will occur
 0-1
 P(A)= probability of A or event

Probability cont.
Looks at the chance of an outcome
 If 2/10 college freshman are on
academic probation after the first year
then I know I have a 20% chance of not
doing well and ending up on probation
F
N
 Closer to the actual probability with
larger sample size

Probability of an event P(event A)

P (event A) = total number of favorable
total number of outcomes

If on average 22 players on a team 64
score at least one touchdown a season,
what is the probability of picking a
student who has scored a touchdown
P(event A)
This is coming in card games
 If there are only 4 card hands that can
beat the leaders cards then what is the
probability that the event of you beating
him will happen?

P(event A) cont…..
P(not A) = 1 - P(A)
 Sum of probabilities will always equal 1
 Probability that an event will not occur is
P(not A)

Statistical Experiment
Any random activity that results in a
definite outcome
 Flip a coin = heads or tails = 2 possible
outcomes = sample space of 2

Probabilities are measured by:
Intuition
 Relative frequency
 Formula for equal likely outcomes

Come up with your own
probability
Think about the topic
 The chances of the outcome
 Think about all of the possible outcomes

2 Key formulas
P(A and B) = P(A) * P(B)
 P(A or B) = P(A) + P(B)
 For any events A and B
P(A or B) = P(A) +P(B) – P(A and B)

PAGE 174
Tree Diagram
In a tennis match you have a 50%
chance of winning.
 If there are 4 rounds til the semis, draw
a tree diagram expressing the
probability of making the semis.

Multiplication rule

If you are purchasing four items, what is
the total combination of items?
A. Item one has 6 choices
B. Item two has 2 choices
C. Item three has 3 choices
D. Item four has 9 choices
Problem
You have 6 schools to choose from
(USC, UCLA, Pepperdine, UCSB,
SDSU, Cal)
 You have 5 degrees to choose from at
each school (Business, Engineering,
Education, Political Science, and
Kinesiology)
 You have 3 possible living situations
(House, Apt, and Dorm)
 What is the probability of P(pepperdine
and Business and Apartment)?

Factorial Notation
For a counting number n
n!=n(n-1)(n-2)……..1
 What is the factorial of 6 choices of
jerseys to wear for practice and then
wearing a different one the next game?

Counting rule for
Permutations
n = number of total population
 r = number of total people to be selected
at one time
 What is (P n, r) for a 12 member
basketball team when you select 5 to
start?
