MATH 218 SI Session (Fall 2008)
Week 3 Worksheet (09/08
–
09/14)
SI Leader: Joy Chen
[email protected]
Prof. Lin & Prof. Song
www.usc.edu/si
Topics Stressed: Probability Trees,
Bayes’ Theorem, Discrete Probability Distribution
1.
On the first day of classes at UCLA, Tommy realized that he was not happy at the school
–
but he wasn’t the
only one. In fact, 55% of the students at the school are not happy. His friend Bob is a happy UCLA student who
chose not to leave, and he represents 37.35% of the population. The probability that an unhappy student will
stay at UCLA is 21%. Assume that all UCLA students who leave transfer to USC.
a.
Design a probability tree and insert the probabilities for each branch.
b.
What is the probability that a student will be unhappy and transfer to USC?
c.
What is the probability of students staying at UCLA?
d.
Tommy decided to transfer to USC. What is the probability that a person who transferred out was
actually happy at UCLA?
2.
A telemarketer sells magazine subscriptions over the telephone.
The probability of no answer is 60%.
If
there is an answer, the probability of 0, 1, or 2 magazine subscriptions is .5, .3, and .2, respectively.
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 Fall '08
 HE
 Conditional Probability, Probability, Probability distribution, Discrete probability distribution, Marble

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