[adamnemecek]

> She finished first. Not by much, and obviously the calculator is the faster choice more often, but she finished first.

This is more of an interface problem I believe.

[WorldMaker]

It's a low level magic trick: she chose the problem. Even supposing she didn't have the answer memorized, she knew exactly what to min/max to favor herself in the challenge.

(A real magician would also work to make sure that the kids thought they chose the problem, but the choice had already been primed for them.)