Duration and Work are not the same thing even though they are both expressed
in units of time so your proposed calculation is invalid. Duration is the
time a task takes while Work is the effort it requires. Duration measures
time while Work measures energy. One person working full time for 8 hours
on a single taks performs 8 man-hours of work. One person working 8 hours
while splitting his attention with another task taking place at the same
time (working 50% units, in other words) does only 4 man-hours of work on
the task in question over the course of its 8 hour duration. Two people
working together for 8 hours on a single task do a total of 16 man-hours for
the task over the course of the 8-hours duration. Looking at each of the
tasks mentioned, only in the first example does Work=Duration and thus will
ActualWork+RemainingWork also equals duration. For the second and third
examples, Work<>Duration and so ActualWork+RemainingWork cannot equal
duration either.
