8-8 Analyzing Decisions Warm Up Lesson Presentation Lesson Quiz Holt McDougal Algebra 2 Holt Algebra 2

Warm Up Find each probability. 1. rolling 2 and tossing heads when rolling a number cube and tossing a coin 1 12 2. rolling an even number or rolling 5 when rolling a number cube 2 3 3. not choosing a multiple of 11 when randomly choosing a whole number from 0 to 99 89 100

Objectives Explain that probability can be used to help determine if good decisions are made. Use probabilities to analyze decisions and strategies.

Vocabulary expected value

In experiments with numerical outcomes, the expected value (EV) is the weighted average of the numerical outcomes of a probability experiment.

Example 1: Finding Expected Value The sides of a six-sided number cube are labeled 1, 1, 3, 3, 9, and 9. A. What is the expected value of the number cube? Value of Side Probability 1 6 3 9

Example 1: Continued 1 6 + E(V) = 3 9 + 1 = E(V) 3 9 6 26 4 B. What is the expected value of rolling two number cubes, one labeled as described in part A and the other labeled 1– 6? 2 3 4 1 +3 5 6 =7 =7.83

Check It Out! Example 1 What is the expected value of rolling the six sided number cube as shown in the net below? Value of Side Probability 1 6 2 3 5

Check It Out! Example 1 continued E(V) = 2 1 6 3 5 + E(V) = 1 + 2 3 5 6 16

Example 2 : Using Expected Value in Real-World Situations On a mountain, it takes Sam 2 hours to climb the southern route, unless there is ice, which increases the time to 4 hours. It takes him 2.5 hours to climb the eastern route, unless there is ice, which increases the time to 3 hours. If the chance of ice is 20% on the southern route and 40% on the eastern route, which route should Sam take if he wants to finish the climb as soon as possible? EV(south) = 0.8(2) + 0.2(4) = 2.4 EV(east) = 0.6(2.5) + 0.4(3) = 2.7 He should take the southern route.

Check It Out! Example 2 Jack can take one of three routes to work each day. Route A takes 16 minutes, Route B takes 10 minutes, and Route C takes 20 minutes. There is a 40% chance he will encounter an accident in Route A, which increases travel time to 25 minutes. There is also a 20% chance he will encounter a traffic jam if he takes Route B, which increases his travel time to 40 minutes. He has a 10% chance of experiencing a delay in Route C, which increases his travel time to 32 minutes. Which route should Jack take to work each day?

Check It Out! Example 2 continued Route A: 0.60(16) + 0.40(25) = 9.6 + 10 = 19.6 minutes; Route B: 0.20(40) + 0.80(10) = 8 + 8 = 16 minutes; Route C: 0.90(20) + 0.1(32) = 21.2 minutes. He should take Route B.

Example 3: The Monty Hall Problem In a TV game show, a car key is hidden in one of five bags. The other bags contain fake keys. Once the contestant picks a bag, the host, knowing where the key is located, opens a bag with a fake key. As the contestant answers questions correctly, he continues to open bags with fake keys until two bags remain: one with the car key and one with a fake key. At this time, he offers the contestant a chance to switch bags. Find the expected value of sticking with the original bag and the expected value of switching bags. EV(sticking) = 1 5 EV(switching) = 4

Check It Out! Example 3 Mikayla is applying to 3 colleges. She makes estimates of her chances of being accepted, and estimates of her chances of receiving financial aid from each, presented below:

Check It Out! Example 3 Continued At which college is she most likely to be both accepted and receive financial aid? College A: 0.75 · 0.30 = 0.225 College B: 0.65 · 0.40 = 0.260 College C: 0.70 · 0.45 = 0.315 She has a higher probability of being accepted in College C with a financial aid.

Lesson Quiz: Part I Find the expected value for number cubes with the given sides. 1. 3, 5, 5, 5, 10, 20 8 2. 1, 5, 5, 5, 5, 6 4.5 3. A secretary can use either the copier in her office or the copier in the hall to make copies of a monthly newsletter. It takes 75 minutes on the copier in her office, unless there is a jam, in which case it takes 110 minutes. It takes 60 minutes on the hall copier, unless it jams, in which case it takes 90 minutes.

Lesson Quiz: Part II The chance of a jam is 15% for the copier in her office and 40% for the copier in the hall. Which copier should she use? EV(office) = 0.85(75) + 0.15(110) = 80.25 EV(hall) = 0.6(60) + 0.4(90) = 72; she should use the hall copier. 4. Benjamin applied for three jobs. He has a 40% chance of being hired at the sandwich shop, a 15% chance of being hired as a mechanic, and a 60% chance of being hired as a driver.

Lesson Quiz: Part III Also, his chances of being hired as a full-time employee are 25% at the sandwich shop, 80% as a mechanic, and 30% as a driver. Which job is he most likely to be hired and be a full-time employee? sandwich shop: 0.4(0.25) = 0.1; mechanic: 0.15(0.8) = 0.12; driver: 0.6(0.3) = 0.18; He is most likely to get both as a driver.