ISSUES IN SOLUTION

In (3), students shouldn't have any trouble realizing that each horizontal sheet of water can in turn be partitioned. Students can then grapple with the problems of how diffusion should work in two or even three dimensions. Some will find it helpful if you suggest considering just one vertical division to have four compartments at first.

It is far more important that the students are allowed time to grapple with modeling issues instead of the method of solution. While the methods involved with solving intermediate parts of the problem are interesting in their own right, if the students are forced to dwell on the details in this problem, they will never get to the major issues of the problem. Thus, use of a CAS such as Mathematica or Maple to solve the DEs quickly is advisable.