Astronomy quiz question: San Luis Obispo, CA equinox

Astronomy 210 Quiz 1, Spring Semester 2011
Cuesta College, San Luis Obispo, CA

On a certain day an observer in San Luis Obispo, CA notices that there are 12 hours between sunrise and sunset. How soon after this date will there be 12 hours between sunrise and sunset?
(A) One month.
(B) Three months.
(C) Six months.
(D) Nine months.
(E) Twelve months.

Correct answer: (C)

12 hours between sunrise and sunset occurs on an equinox, either in March (vernal) or September (autumnal). The time between any type of equinox ("how soon after this date") is six months.

Section 30674
(A) : 5 students
(B) : 5 students
(C) : 25 students
(D) : 1 student
(E) : 6 students

"Success level": 62% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.69

Section 30676
(A) : 3 students
(B) : 3 students
(C) : 34 students
(D) : 0 students
(E) : 10 students

"Success level": 71% (including partial credit for multiple-choice)
Discrimination index (Aubrecht & Aubrecht, 1983): 0.42