Lesson 30: Probability

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Lesson 30 Probability

• Objectives
• Determine the probability of drawing two red
  balls (without replacement) from an urn with 3
  red balls and 4 green balls
• Determine the probability of being dealt a royal
  flush

• Outline
• Examples of Probability

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Announcements

• Book report Due April 28
• Exam 3 April 23
• Final Exam Monday, May 12 1-3p

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Coin Toss

• You flip a coin thrice. Find the following
• P(E) where E is the event of getting a heads on
  the first flip and a tails on the second flip and
  a heads or tails on the third flip.
• P(F) where F is getting one head and two tails in
  the three flips

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Monty Hall
5
Doorbell

• A family has 2 children. You ring the doorbell
  of the house and a girl answers the door. What
  is the probability that the other child in the
  family is also a girl? Assume that the children
  are not twins, the probability of the birth of a
  girl or a boy are independent events, and the
  probability of the birth of a child of either sex
  is 1/2.

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True/False

• A T/F quiz has 10 questions. If you randomly
  answer each question, what is the probability of
  getting at least 70?

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Passwd

• A computer password consists of 5 lowercase
  letters.
• Find p(E) where E is the event that the passwd
  starts with c
• Find p(F) where F is the event that the passwd
  contains no vowels.

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Probability

• For non-equally likely outcomes
• 0lt p(s) lt 1 for every s in S
• The sum of all p(s) in S 1

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Uniform Distribution

• A set has n elements. The uniform distribution
  assigns the probability 1/n to each element of S

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Definition Review

• Event successful trial
• Sample Space set of possible outcomes
• Experiment a trial yielding a result

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Probability

• The probability of the event E is the sum of the
  probabilities of the outcomes in E.
• That is
• p(E) sump(s)