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Published byJerome McDaniel Modified over 8 years ago

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An outcome is a possible result An event is a specific outcome Random means all outcomes are equally likely to occur or happen. random = fair A favorable event is the outcome you’re looking for

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The probability that an event will happen is a number between 0 and 1: A probability of 0 means the event will definitely NOT happen. A probability of 1 means the event definitely WILL happen. All other probabilities are between 0 and 1

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0 Impossible 1 Definite 50-50 chance Probability The probability that an event will happen can be also described as a percent. 0 Impossible 100% Definite50%

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Probability is the chance that some event will happen. It can be written as a ratio. # of favorable outcomes (what you want) total # of possible outcomes

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There are 2 types of probabilities: 1) Theoretical 2) Experimental Theoretical probability is calculated. # of favorable outcomes # of possible outcomes Experimental probability is based on actual results (something you did and counted).

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Now turn to page 383 and try Guided Practice problems 1 and 2

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Guided Practice problem 1 You roll a number cube (dice) 100 times. Your results are given in the table below. Number123456 Rolls171520161418 What is the experimental probability of rolling a number greater than 3? Remember, experimental probability is based on something that you actually did! So use the numbers in the chart. Probability = number of favorable outcomes number of total outcomes P = 16 + 14 + 18________ 17 + 15 + 20 + 16 + 14 + 18

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Guided Practice problem 1 continued You roll a number cube (dice) 100 times. Your results are given in the table below. Number123456 Rolls171520161418 What is the theoretical probability of rolling a number greater than 3? Remember, theoretical probability is based the possible outcomes. Probability = number of favorable outcomes number of total outcomes

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Guided Practice problem 1 continued You roll a number cube (dice) 100 times. Your results are given in the table below. Number123456 Rolls171520161418 So the experimental probability of rolling a number greater than 3 was 48% based on the experiment that was done. Theoretical probability or calculated probability was 50%. The experimental probability becomes more accurate or closer to the theoretical probability when there are more trials.

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Guided Practice problem 2 Use the information in Example 3. About how many buttons would you expect to be defective in a shipment of 25,000 buttons? A company manufactures buttons. A quality control inspector finds 2 defective buttons in a batch of 300 buttons. About how many buttons would you expect to be defective in a shipment of 25,000 buttons? Use cross products to find the answer. 300x = 50,000 divide both sides by 300 About 167 buttons

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Independent Events – events that do not effect each other To calculate the probability of 2 independent events: Find the probability of each one, then multiply Ex. What is the probability of rolling a 1 and then rolling a 2 on a standard die. P (1) = P (2) = P (1 then 2) = Probability of Compound Events

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Let’s try some: Suppose you roll a red die and a blue die. What is the probability that you will roll a 5 on the red and a 1 or 2 on the blue. The probability of rolling a 5 is The probability of rolling a 1 or a 2 is To find the probability of BOTH, multiply them:

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There is a bag of marbles. There are 4 white, 3 black, 8 purple, 2 red, and 8 green. Find the probability of choosing a purple, then a red after replacing the 1 st marble.

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There is a bag of marbles. There are 4 white, 3 black, 8 purple, 2 red, and 8 green. Find the probability of choosing a purple, then a red without replacing the 1 st marble.

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If you are feeling confident about simple probability, you can get a head start on the classwork. Pages 383 – 385 1-23 Compound probability will NOT be on the test! If you don’t get it, don’t worry…we will talk about it in class.

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