In this paper we analyse 11 pairs of pre-service primary teachers’ solutions to twoFermi problems. The solutions were expressed using the descriptive and analytic FPATframework (Fermi problem Activity Template), and our analysis focus on characterizingthe FPAT representations produced by the pre-service teachers. The results show thatalmost half of the produced FPATs in principle solved the problems but that only threesolutions provided enough detail to be practically implementable. Multiple keyconstructs were used to structure the solutions in the first problem, but not so in thesecond problem. The variation of different activities and ways of working suggested insolving the sub-problems in the two problems also differ in a significant way.