Following are four sets of most optimistic, most likely, and most pessimistic times (in weeks) for an activity. Which one of the four sets will have a mean estimated time equal to the most likely time?
A) 1, 9, 9
B) 1, 5, 9
C) 1, 1, 9
D) 1, 5, 5

Question

Quizplus · Accepted Answer

For the mean estimated time to be equal to the most likely time, the optimistic time and pessimistic time must be equidistant from the most likely time. Therefore, the difference between the optimistic time and most likely time should be the same as the difference between the most likely time and pessimistic time. 
Set B satisfies this condition as (5-1) = (9-5), while the other sets do not.

Following Are Four Sets of Most Optimistic, Most Likely, and Most