Astronomy quiz question: moon phase, overhead to setting?

Astronomy 210 Quiz 1, spring semester 2012
Cuesta College, San Luis Obispo, CA

[Version 1]
The waxing gibbous moon is directly overhead at 9:00 PM. What phase will the moon have when it sets? Clearly circle your answer below.

Correct answer: (A) (Waxing gibbous.)

Section 30676
Exam code: quiz01sH0p
(A) : 26 students
(B) : 3 students
(C) : 6 students
(D) : 0 students
(E) : 3 students
(F) : 1 student
(G) : 6 students
(H): 0 students
(No response : 3 students

Success level: 57% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.48

[Version 2]
The waning gibbous moon is directly overhead at 3:00 AM. What phase will the moon have when it sets? Clearly circle your answer below.

Correct answer: (G) (Waning gibbous.)

The moon will take approximately four weeks to go through all eight of its phases, such that it will take approximately one week to go through two phases, or approximately half of a week to go to the next consecutive phase. As the moon takes approximately 12 hours from moonrise to moonset, the phase it has while overhead will be the same phase as it sets six hours later.

Section 30674
Exam code: quiz01n3Wb
(A) : 2 students
(B) : 0 students
(C) : 4 students
(D) : 1 student
(E) : 12 students
(F) : 1 student
(G) : 15 students
(H) : 0 students

Success level: 46% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.56