1. Probability

2. Probability: Likeliness that an event will occur

3. Probability = # of Successes Total # of Possibilities

4. Probability = ** Successes DO NOT have to be “good” things # of Successes Total # of Possibilities

5. Example 1: A bag of marbles contains 4 blue marbles, 6 yellow marbles, 12 red marbles, and 2 green marbles. If a marble is drawn from the bag at random, what is the probability that it will be a green marble?

6. Example 2: A study finds that out of 230 drivers under the age of eighteen, 176 use their cell phones while driving. What is the probability that a driver under the age of eighteen uses their cell phone while driving?

7. Practice: A box of chocolates contains 4 cherry cordials, 6 caramels, 3 coconut creams, 2 peanut butter filled, and 9 chocolate truffles. If all of the candies have the same appearance, what is the probability of selecting a caramel from the box?

8. Probability can also be used to determine the number of successes.

9. # of Successes = Probability ∙ Total #

10. Example 3: If the probability of drawing a green marble from a bag containing 2,000 marbles is 17%, how many green marbles does the bag contain?

11. Practice: Kim is selling girl scout cookies. If Kim sells 231 boxes of cookies, and ⅓ of all her sales were Thin Mint cookies, how many boxes of Thin Mint cookies did Kim sell?

12. Mutually Exclusive Events

13. Mutually Exclusive Events: Two events that cannot happen at the same time - Usually involves the word “or”

14. Mutually Exclusive Events: Two events that cannot happen at the same time - Usually involves the word “or” Examples:

15. Calculating Mutually Exclusive Probabilities: To find the probability of one or the other mutually exclusive events occurring, add the probabilities together.

16. Example 1: You roll a six-sided die. What is the probability of obtaining a 5 or a 6?

17. Example 2: A bag of marbles contains 4 blue marbles, 6 yellow marbles, 12 red marbles, and 2 green marbles. If a marble is drawn from the bag at random, what is the probability that it will be a green or yellow marble?

18. Practice: The school has 306 freshmen, 254 sophomores, 261 juniors, and 258 seniors. What is the probability that a student selected at random will be a junior or senior?