Stock prices. For the 71 trading days from January 3, 2017, to April 18, 2017, the daily closing price of IBM stock (in $) is well modeled by a Normal model with mean

$174.85 and standard deviation $4.51. According to this model, what is the probability that on a randomly selected day in this period the stock price closed

a) above $179?

b) below $184?

c) between $161 and $188?

d) Which would be more unusual, a day on which the stock price closed above $180 or below $165?