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Working with the Normal Distribution and z scores: Practice Problems
1) Assume that professors’ evaluation scores are normally distributed with a mean of 100 and a
standard deviation of 25 (ie. µ=100 and ó = 25). What is the probability that a professor would
get an evaluation above 115?
Answer: .2743
2) If IQ scores are normally distributed with a mean of 100 and a standard deviation of 20, then
the probability of the persons having an IQ score of at least 130 is
a) .4332
b) .3000
c) .9332
d) .0668
3) A bank finds that the balances for its customers and their savings accounts are normally
distributed with a mean of $500 and a standard deviation of $50. The probability that a randomly
selected account has a balance of more than $600 is
a) .4772
b) .0228
c) .9772
d) .0000
4) The lifetime of a certain brand of tires is normally distributed. The average lifetime of a tire is
50,000 miles with a lifetime standard deviation of 8400 miles. The probability that a randomly
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 Cohn,SaulUri

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