The bridge and the torch
Four people, one torch, and a plan you can try.
Four people take 1, 2, 5 and 10 minutes to cross. They must carry the torch. One or two cross at a time; a pair takes the slower time. Get everyone across, then try for a 17-minute plan if you like.
What you will practise: Plan returns and compare valid plans.
Think it through together
One person proposes a strategy; the other asks “why?” and looks for a case where it fails. Then swap roles. No names or speed competition needed.
Before viewing the explanation: what do we know, what are we assuming, and how would we check the result?