The author surveyed students in one of his statistics classes about the number of hours they worked per week. The density histogram in Fig. 17 describes their responses. For a randomly selected student in the class, let X be the number of hours the student works per week.
a. Find P(X ≥ 20).
b. Find P(X< 15).
c. Find P(10 ≤ X < 25).
d. From inspecting the density histogram, a student concludes that 33% of all statistics students in the United States work less than 5 hours per week. What would you tell the student?
e. A counselor advises that part-time students work less than 25 hours per week and that full-time students work less than 15 hours per week. What percentage of the class did not follow this guideline for certain?