A theater box office sold an average (arithmetic mean) of 63 tickets per staff member to a particular movie. Among the daytime staff, the average number sold per member was 78, and among the evening staff, the average number sold was 60. If there are no other employees, what was the ratio of the number of daytime staff members to the number of evening staff members?  Choose the correct choice from the following answers
A) 2 : 3  B) 1 : 4  C) 1 : 5  D) 6 : 11  E) 4 : 7

Rationale: deviation from the mean for the daytime staff = 78 - 63 = 15 . deviation from the mean for the evening staff = 63 - 60 = 3 . thus , the ratio of the number of daytime staff members to the number of evening staff members is 3 : 15 = 1 : 5 . the answer is c .
Answer: C