Probability of Compound Events
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Transcript Probability of Compound Events
Probability of Compound
Events
Review of Simple Probability
The probability of a simple event is a ratio of the
number of favorable outcomes for the event to the
total number of possible outcomes of the event.
The probability of an event a can be expressed as:
number of favorable outcomes
Pa
total number of possible outcomes
Find Outcomes of simple events
For Simple Events – count the outcomes
Examples:
One Die- 6 outcomes
One coin- 2 outcomes
One deck of cards- 52 outcomes
One fair number cube- 6 outcomes
Finding Outcomes of more than one
event
The total outcomes of each event are found
by using a tree diagram or by using the
fundamental counting principle.
Example:
At football games, a student concession
stand sells sandwiches on either wheat or rye
bread. The sandwiches come with salami,
turkey, or ham, and either chips, a brownie,
or fruit. Use a tree diagram to determine the
number of possible sandwich combinations.
Tree diagram with sample space
Answer
Using the fundamental counting principle
bread x meat x side
2 x
3 x 3 = 18 outcomes
Probability of Compound Events
A compound event consists of two or more
simple events.
Examples:
rolling a die and tossing a penny
spinning a spinner and drawing a card
tossing two dice
tossing two coins
Compound Events
When the outcome of one event does not
affect the outcome of a second event, these
are called independent events.
The probability of two independent events is
found by multiplying the probability of the
first event by the probability of the second
event.
Compound Event Notations
Independent Events
Example: Suppose you spin each of these two spinners. What
is the probability of spinning an even number and a vowel?
1
P(even) =
(3 evens out of 6 outcomes)
2
1
(1 vowel out of 5 outcomes)
P(vowel) =
5
1 1 1
P(even, vowel) =
2 5 10
1
6
P
S
5
2
O
T
3
4
R
Slide 10
Independent Events
Find the probability
P(jack, factor of 12)
4
52
5
x
8
5
=
104
Slide 11
Independent Events
Find the probability
P(6, not 5)
1
6
5
x
6
5
=
36
Slide 12
Probability of Compound events
P(jack, tails)
4 1
4
( )
0.04 4%
52 2
104
Dependent Event
What happens during the second event
depends upon what happened before.
In other words, the result of the second event will
change because of what happened first.
The probability of two dependent events, A and B, is equal to the
probability of event A times the probability of event B. However,
the probability of event B now depends on event A.
P(A, B) = P(A) P(B)
Slide 14
Dependent Event
Example: There are 6 black pens and 8 blue pens in a jar. If you
take a pen without looking and then take another pen without
replacing the first, what is the probability that you will get 2
black pens?
P(black first) =
6
3
or
14
7
5
P(black second) =
(There are 13 pens left and 5 are black)
13
THEREFORE………………………………………………
P(black, black) =
3 5
15
or
7 13
91
Slide 15
Practice
1. P(heads, hearts) =
2. P(tails, face card) =
Your turn
Create your own independent compound
event problem. Then, exchange with your
seat partner.