Suppose we want a 90% confidence interval for the average amount spent on
entertainment (movies, concerts, dates, etc.) by Freshman in their first semester at a
large university. The interval is to have a margin of error of $2, and the amount spent
has a normal distribution with a standard deviation s = $30. The number of
observations required is closest to
A) 25.
B) 30.
C) 609.
D) 865.