Another explanation for our findings can be found in the kind of multiple solution that was
prompted in the classroom. The influence of prior knowledge might be limited because students
did not need special mathematical knowledge to increase the number of solutions they developed
when the solutions were based on different assumptions about missing data such as the position of
the fire vehicle in the Fire-brigade task. This assumption is in line with a finding from our
previous case study: Students who found one solution often had only minor difficulties in
constructing a second solution using the same mathematical model and the same mathematical
procedure to solve modelling tasks with vague conditions (Schukajlow & Krug, 2013a)