Transcript Probability

½ = 50%
Probability
What is probability?
How is probability written?
How is probability calculated for independent events?
Principles of Probability
Probability:
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Number describing how likely an event will
occur
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0 = event is impossible
1 = event is certain (will happen for sure)
Event:
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Something that happens
An outcome
Every event has a probability (likelihood) of
happening
Expressing probability
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Can be written as a fraction or percent
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Writing as a fraction:
Probability =
desired event
all possible events
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Ex. Probability of a coin flip landing on heads
Probability = 1 (only one side is heads)
2 (two sides on a coin)
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Writing as a percent: divide top by bottom
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½ = .5 = 50%
Principles of Probability
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2 types of event:
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Independent = Results do not affect other
events
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Consecutive dice rolls or coin flips
Dependent = Results do affect other events
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Pulling consecutive cards from a deck (without
replacing)
You Try
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What is the probability of rolling a 6 on a dice?
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1/6
1 side has a 6 (desired outcome = 1)
There are 6 total sides (total outcomes = 6)
What is the probability of rolling an even number on
a dice?
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½
3 sides have even numbers: 2,4,6 (desired outcome = 3)
There are 6 total sides (total outcomes = 6)
3/6 reduces to 1/2
You Try
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What is the probability of randomly pulling a queen
out of a deck of cards?
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1/13
4 queens (desired outcome = 4)
There are 52 cards in a deck (total outcomes = 52)
4/52 reduces to 1/13
What is the probability of rolling a 12 if two dice are
rolled?
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1/36
1 way to roll a 12: two sixes (desired outcome = 1)
There are 36 ways the dice can land (total outcomes =
36)
Two dice probabilities