An engineering student who is about to graduate decided to survey various firms in Silicon Valley to see which offered the best chance for early promotion and career advancement. He surveyed 30 small firms (size level is based on gross revenues), 30 medium-sized firms, and 30 large firms, and determined how much time must elapse before an average engineer can receive a promotion.

a. Can the engineering student conclude that speed of promotion varies between the three sizes of engineering firms?

b. If differences exist, which of the following is true? Use Tukey’s method.

i. Small firms differ from the other two.

ii. Medium-sized firms differ from the other two.

iii. Large firms differ from the other two.

iv. All three firms differ from one another.

v. Small firms differ from large firms.