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probability and normal distribution

25. A major department store has determined that its customers charge an average of $500 per month with a standard deviation of $80. Assume the amounts of charges are normally distributed.

a. What percentage of customers charges more than $380 per month?

P(x > 380) = 1- p(x<380)

(P(x<380) = z value = x - mean / std dev
Z Value = (380 - 500)/80 = -1.5

P(x<380) = 0.0668 How do I get this number? I get how to get the z value but where does the .0668 come from? I looked on my table in the book but I can't find .0668 anywhere.

P(x > 380) = 1- p(x<380)
= .9331 or 93.31%

Solution Summary

The solution investigates the normal distribution data from a department store.

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