2.7 Probability of Compound Events
Compound Event - combining two or more
separate events
1. Independent Events
2. Dependent Events
Independent Events
Events that do not influence each other.
RULE:
Probability of TWO independent events
IF A and B are independent events, P(A and B) = P(A) * P(B)
Suppose you roll two dice, one
before the other on your desk.
Does the first die have any affect
the second?
P(3 and 5)
P(4 and 4)
P(both even)
P(both less than 3)
Determining Probability of
Independent Events
Suppose you pull two tiles
from the bag and replace the
first tile after you draw it.
x
W Y
x
x
W
W
P(X and X)
Y
P(Y and X)
Z
Y
x
P(Z and W)
Dependent Events
Events that do influence each other, the occurrence of
the first event affects the occurrence of the second.
RULE: Probability of TWO Dependent Events
If A and B are dependent events,
P(A then B) = P(A) * P(B after A)
Now we are going to draw the letter, but NOT replace it after
each trial...
P(X then X)
x
W
Y
Y
W
P(Z then W)
Z
x
x
W
P(Y then X)
Y
x
Determining
Probability of
Dependent Events
Mutually Exclusive Events
Events that cannot occur at the same
time.
RULE:
Probability of TWO mutually exclusive events
IF A and B are mutually exclusive events, P(A or B) = P(A) + P(B)
P(orange or blue)
P(green or red)
P(yellow or green)
Probability Activity
Each group will get a slip of paper with a
probability problem.
Your task is to:
• Write the number of your event.
• Determine if the situation
describes independent, dependent, or
mutually exclusive events.
• Calculate the probability on the paper.
Homework:
2.7 - Pg. 104 2, 4, 10, 12, 16, 20, 30,
38, 40