Play it · Ages 13–14
Twelve Coins
Heavier or lighter — you are not told which. Three challenges — each one changes what you have to do, not just how many of it there are. Nothing is timed and nothing is scored.
0 of 3 solved
One coin is fake. Heavy or light, you do not know. Three weighings.
Not knowing the direction doubles the answers you have to tell apart.
Nine coins
left pan
empty
right pan
empty
Tap a coin: tray → left pan → right pan
0 / 3 used
Ten minutes of stuck counts as the work.
Now do it away from the screen
The board is the warm-up. The year page has the same problem on paper, the hint ladder, the answer, the five-day week and three questions nobody can mark — which is where the twenty-five minutes actually go.