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4.20 Chicken Pox, Part II: We learned in another exercise that about 90% of American adults had chickenpox before adulthood. We now consider a random sample of 120 American adults.

(a) How many people in this sample would you expect to have had chickenpox in their childhood?
(please round to two decimal places)

(b) What should the standard deviation of number of people having had chickenpox in such samples be?
(please round to four decimal places)

(c) Would you be surprised if there were 105 people who have had chickenpox in their childhood?

Yes, being surprised is fun!
No, 105 is within two standard deviations of the expectation.
Yes, 105 is more than two standard deviations from the expected number
Yes, it should be exactly the number I got for the first question

(d) What is the probability that 105 or fewer people in this sample have had chickenpox in their childhood? (please round to four decimal places)

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