Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 1 Probability: Living With The Odds 7

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 2 Unit 7B Combining Probabilities

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 3 Two events are independent if the outcome of one does not affect the probability of the other event. If two independent events A and B have individual probabilities P(A) and P(B), the probability that A and B occur together is P(A and B) = P(A) P(B). This principle can be extended to any number of independent events. And Probability: Independent Events

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 4 Example What is the probability of rolling three 6s in a row with a single die? Solution

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 5 Two events are dependent if the outcome of one affects the probability of the other event. The probability that dependent events A and B occur together is P(A and B) = P(A) P(B given A) where P(B given A) is the probability of event B given the occurrence of event A. This principle can be extended to any number of dependent events. And Probability: Dependent Events

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 6 Example A three-person jury must be selected at random from a pool that has 6 men and 6 women. What is the probability of selecting an all-male jury? Solution The probability that the first juror is male is 6/12. If the first juror is male, the remaining pool has 5 men among 11 people. The probability that the second juror is also male is 5/11 and so on.

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 7 Two events are non- overlapping if they cannot occur together, like the outcome of a coin toss, as shown to the right. For non-overlapping events A and B, the probability that either A or B occurs is shown below. P(A or B) = P(A) + P(B) This principle can be extended to any number of non-overlapping events. Either/Or Probabilities: Non-Overlapping Events

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 8 Example Suppose you roll a single die. What is the probability of rolling either a 2 or a 3? Solution The probability of rolling either a 2 or a 3 is 1/3.

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 9 Two events are overlapping if they can occur together, like the outcome of picking a queen or a club, as shown to the right. For overlapping events A and B, the probability that either A or B occurs is shown below. P(A or B) = P(A) + P(B) – P(A and B) This principle can be extended to any number of overlapping events. Either/Or Probabilities: Overlapping Events

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 10 What is the probability that in a standard shuffled deck of cards you will draw a 5 or a spade? Solution These are overlapping events. P(A or B) = P(A) + P(B) – P(A and B) P(5 or spade) = P(5) + P(spade) – P(5 and spade) = 4/ /52 – 1/52 = 16/52 = 4/13 Example

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 11 The At Least Once Rule (For Independent Events) Suppose the probability of an event A occurring in one trial is P(A). If all trials are independent, the probability that event A occurs at least once in n trials is shown below. P(at least one event A in n trials) = 1 – P(not event A in n trials) = 1 – [P(not A in one trial)] n

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 12 Example Use the at least once rule to find the probability of at least one head when you toss three coins. Solution In this case, the event A is getting heads on one toss, and for three coins n = 3. Therefore, the at least once rule tells us that P(at least one H in 3 tosses) = 1 – P(no H in 3 tosses) = 1 - [P(no H in 1 toss)] 3

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 13 Example (cont) The probability of getting no heads in one toss is 1/2, so our final result is

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 14 Example You purchase 10 lottery tickets, for which the probability of winning some type of prize on a single ticket is 1 in 10. What is the probability that you will have at least one winning ticket among the 10 tickets? Solution The probability of winning with any one ticket is 0.1, the probability of not winning with one ticket is 1 − 0.1 = 0.9.

Copyright © 2015, 2011, 2008 Pearson Education, Inc. Chapter 7, Unit B, Slide 15 Example The probability of winning at least once with ten tickets is P(at least one win10 tickets) = 1 – [P(not winning1] 10 = 1 − [0.9] 10 ≈ 0.651