To my mind this question is clearly unanswerable.
I was therefore shocked to read, in an old but interesting book (Redish, 2003) that many schoolchildren try to find an answer. (“The teacher, wouldn’t give me a problem that has no solution”).
Furthermore they frequently come up with an answer of 25. (“There are only two numbers to work with: 5 and 125. Adding, multiplying and subtracting them doesn’t give something that could be an age. Only dividing gives a plausible answer.”)
I find that worrying. It links to the fact that true problem solving is about more than finding the right formula to use by trial and error and then manipulating it. I’m really not sure that many of our students develop the problem solving skills that we want them to develop; skills that would help in the real world as well as in passing physics exams.
We want our students to be independent and reflective learners, understanding the relevance of what they learn for the real world. How do we encourage these behaviours? I don’t know, but I find it worrying that Joe Redish goes on to report that so called unfavourable behaviours (Hammer, 1996) actually increased after instruction, at the expense of favourable behaviours.
Hammer, D. (1996) More than misconceptions: Multiple perspectives on student knowledge and reasoning, and an appropriate role for education research, Am J. Phys, 64, 1316-1325.
Redish, E.F. (2003) Teaching physics with the Physics Suite. Wiley.