Day 3 ­ Define and Use Probability.notebook
Unit E ­ Day 3
Objective: To define and use probability (D.4.B)
Probability: The probability of an event is a number from 0 to 1
that indicates the likelihood the event will occur, as shown on
the number line below. Probabilities can be written as
fractions, decimals or percents.
event is more likely not to occur
P=0
Wehrle event is more likely to occur
P = 0.5
P=1
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Day 3 ­ Define and Use Probability.notebook
Theoretical Probability of an Event
When all the outcomes are equally likely, the
theoretical probability that event A will occur is:
P(A) =
Number of outcomes in event A
Total Number of outcomes
Examples:
1. You roll a standard six­sided dice. Find the probability of
(a) rolling a 5
(b) rolling an even number
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Day 3 ­ Define and Use Probability.notebook
2. You have an equally likely chance of choosing any integer
from 1 ­ 20.
a.) Find the probability of choosing a perfect square.
b.) Find the probability that a factor of 30 is chosen.
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Day 3 ­ Define and Use Probability.notebook
Experimental Probability
When an experiment is performed that consists of acertain
number of trials, the experimental probability of an event A is
given by:
P(A) =
Number of trials where A occurs
Total number of trials
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Day 3 ­ Define and Use Probability.notebook
Odds in Favor or Against an Event
When all outcomes are equally likely, the odds in favor
of event A and the odds against event A are defined as:
Odds in favor of
event A
:
Number of outcomes in A
Number of outcomes not in A
Odds against
event A
:
Number of outcomes not in A
Number of outcomes in A
Note: We can write odds in favor or against an event in the
following two forms:
a:b or a
b
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Day 3 ­ Define and Use Probability.notebook
Examples of odds
A card is drawn from a standard deck of 52 cards. Find
a.) Odds in favor of drawing a 10
b.) Odds against drawing a club
c.) Odds in favor of drawing a heart
d.) Odds against drawing a queen
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Day 3 ­ Define and Use Probability.notebook
Let's mix the problems up:
There are 40 marbles in a bucket. 7 are red, 9 are blue, 12
are purple, 3 are yellow, 2 are orange, and 7 are tie­dye.
a.) What is the probability of picking an orange marble
out of the bucket?
b.) What is the probability of picking a red marble out of
the bucket?
c.) What are the odds in favor of picking a tie­dye marble?
d.) What are the odds against a purple marble?
e.) What is the probability of picking a yellow marble? Wehrle 7