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Probability
Probability: Likeliness that an event will occur
Probability = # of Successes
Total # of Possibilities
Probability =
** Successes DO NOT have to be “good” things
# of Successes
Total # of Possibilities
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?
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?
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?
Probability can also be used to determine the number of successes.
Probability can also be used to determine the number of successes.
# of Successes = Probability Total #∙
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?
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?
Mutually Exclusive Events
Mutually Exclusive Events: Two events that cannot happen at the same time
- Usually involves the word “or”
Mutually Exclusive Events: Two events that cannot happen at the same time
- Usually involves the word “or”
Examples:
Calculating Mutually Exclusive Probabilities:
To find the probability of one or the other mutually exclusive events occurring, add the probabilities together.
Example 1:
You roll a six-sided die. What is the probability of obtaining a 5 or a 6?
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?
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?
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