Addition and Multiplication Rule of Probability

Let's check for understanding from this week's topics.

Learning
Target

• Students will learn how to utilize

the multiplication rule to
calculate probabilities of when a
second event is impacted by
what happens during the first
event

Calculating Probabilities

WHEN WE CALCULATE PROBABILITIES INVOLVING
ONE EVENT AND ANOTHER EVENT OCCURRING,

WE MULTIPLY THEIR PROBABILITIES.

IN SOME CASES, THE FIRST EVENT HAPPENING

IMPACTS THE PROBABILITY OF THE SECOND
EVENT. WE CALL THESE DEPENDENT EVENTS.

IN OTHER CASES, THE FIRST EVENT HAPPENING

DOES NOT IMPACT THE PROBABILITY OF THE
SECONDS. WE CALL THESE INDEPENDENT

EVENTS.

We can represent this
concept with a tree
diagram like the one
shown.

We multiply the
probabilities along
the branches to
find the overall
probability of one
event AND the
next even
occurring.

For example, the probability of
getting two "tails" in a row would be:

When two events are independent,
we can say that

Be careful! This formula only applies
to independent events.

Note: P(B) = 1 – P(B’)

What is the probability of pulling a King and Queen out of a standard
deck of playing cards? Note: The cards are not replaced once one is
pulled out of the deck.

Lesson Recap