1. Introducing Conditional Probability (4.2.1)
March 3rd, 2017

2. number of outcomes in (A and B)
Vocabulary & Notation
*Conditional Probability: The probability that event B occurs, given that event A has already occurred, written as
“the probability of B given A”
number of outcomes in (A and B)
number of outcomes in A
*Look for key parts of phrases, like “find the probability of ____ given _____” or what is the probability of ______if _______”.

3. Ex. 1: Nate rolls a pair of 6-sided dice (also called number cubes)
Ex. 1: Nate rolls a pair of 6-sided dice (also called number cubes). What is the probability that both numbers are prime if their sum 7?

4. Independent Events & Conditional Probability
*Recall that for Independent Events, we know
Therefore,

5. Ex. 2: Masanori rolls a number cube 3 times
Ex. 2: Masanori rolls a number cube 3 times. Consider the following events.
A: The first roll is an even number.
B: There are at least two even numbers.
Determine if A and B are independent events.

6. Ex. 3: Last year in Mrs. MT’s Calculus class 92% of students received a passing score on the Advanced Placement exam. That same year, 25% of those students also received an A in the Calculus class. What is the probability that a student who passed the AP Exam also got an A in the class?