Download LESSON 12

Probablity Day 9 Notes - Independent and Dependent Events
Goal: Study independent and dependent events.
Warm-up:
1) There are three red gumballs and 4 blue gumballs in a container. If you reach in and
randomly pick one gumball, what’s the probability that you will choose a red gumball?
2) If you throw the red gumball that you chose in problem one back in, what’s the
probability that you will randomly pick another red gumball?
3) If you DO NOT throw the red gumball back in, what’s the probability that you will
randomly pick another red gumball?
4) Talk to your neighbor and in your own words, define the word independent.
5) Talk to your neighbor and in your own words, define the word dependent.
Goal: Study independent and dependent events.
Vocabulary
Independent events:
Dependent events:
EXAMPLE 1 - Independent and Dependent Events
Tell whether the events are independent or dependent.
A) You toss a coin. Then you toss the coin again.
The result of the first toss __________________ affect the result of the second toss, so the events
are ___________________________________.
B) Your teacher randomly chooses a student to go to the board. The student remains at the
board when your teacher randomly chooses another student to go to the board.
There is one fewer student to choose from when the teacher chooses another student, so
the events are ____________________________________.
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Probability of Independent and Dependent Events
Words For multiple events, the probability that both events occur is the
_______________________________ of the probabilities of the events.
Algebra If events A and B are independent, then P(A and B) = ____________________________.
EXAMPLE 2 – Finding Probability of Independent Events (a review)
History Report: Each student in your history class is to write a report on one of the 50 United
States. Each student randomly chooses a state. What is the probability that you and the
student who sits behind you randomly choose Illinois? Randomly chooses the same state?
EXAMPLE 3 - Finding Probability of Dependent Events (new)
Carnival You are playing a balloon popping game at a carnival. There are 19 red, 15 blue,
12 yellow, and 14 green balloons. You randomly pop balloons by throwing darts at them.
What is the probability that the first two balloons you pop are yellow?
Now You Try It! Find the probability.
1) You roll a number cube twice. Find the probability of getting two odd numbers.
2) In Example 3, find the probability that the first two balloons you pop are blue.
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