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Exam Review Session
Probability
A random sample
(1) Each individual has an equal chance of being selected.
(2) If more than one individual is selected, the probabilities must stay constant for
all selections.
Example:
A jar contains 10 black marbles and 30 white marbles.
a.
What is the probability of obtaining a black marble?
b.
After taking 1 black marble out, what is the probability of obtaining another
black marble?
c.
If we take a random sample of n=3 marbles from the jar and the first two are
white, what is the probability that the third would be black?
Remember: a random sample requires replacement
.
Answer:
a. 10/40 = .25
b. 9/39 = .23
c. 10/40 = .25
The normal approximation to the binomial distribution
The binomial distribution will approximate a normal curve as sample size increases.
pn
the number of times category A occurs
qn
the number of times category B occurs
Specifically, if both pn and qn are either equal to or greater than 10, the distribution
will approximate a normal curve.
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 Fall '09
 Shinkareva

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