Presuming this is using the North American floor conventions (which I presume to be the case based on University of Waterloo being in Canada, which according to

Presuming this is using the North American floor conventions (which I presume to be the case based on University of Waterloo being in Canada, which according to wikipedia is likely to use the same naming conventions as America[1]), wouldn't it be better to optimize example 3 by having the second elevator on the seventh floor? This means floors 8-12 and 6-2 are only five floors away. If you station the second elevator on floor 6, then floor 12 is six spots away, and floor 2 four spots away. Its definitely much more complex than that (e.g. the ground floor elevator could take people down from floors 2 & 3 or something, depends on time of day, etc.), but if the author's intention was to station one elevator at ground level and another in the middle, floor 7 is the better choice. [1] http://en.wikipedia.org/wiki/Storey#North_American_scheme http://en.wikipedia.org/wiki/Storey#North_American_scheme