Asking a student to find the solution to a problem creates high cognitive load that she may end up making a lot of mistakes. This is especially true when the problem requires many sub problems to be solved, and students tend to make many more errors in these sub goal stages than at the final goal stage. This effect is called the stage effect.
An alternative to help students learn problem solving is to ask them to find the value of as many unknowns as possible, rather than finding a value for a specific goal. As an example, given a programming assignment, students are asked what are the unknowns rather than asking them to create a final program. This can be open ended and the students may go off on a tangent if not properly guided. Of course, no one would hire these students if all they can do is to come up with unknowns(!), but this strategy can be used as a scaffolding device to help students connect what they already know and what we want them to know. New knowledge can be built up as the unknowns are identified, and how these unknowns are related to what has already been learned.
Ayres, P. (1993). Why Goal-Free Problems Can Facilitate Learning. Contemporary Educational Psychology. 18, pp 376 - 381.