A professor is trying to figure out how many custom books to order for his class of 25 students. In the past, the number of students buying books has shown the following demand pattern: Number of students who bought a book, Percentage of Observations 16 or fewer, 0% 17 4% 18 15% 19 17% 20 18% 21 26% 22 10% 23 6% 24 4% Suppose each custom book costs the professor $ 12 to print, and he sells the books to the students for $ 35 each. Excess books are sold for $3 each and have to be shipped to those buying an excess book. The shipping cost is $1 per book. How many books should the professor plan on ordering? Round to nearest whole number. Blank 1