Queen Ratnamanjuri's locker puzzle, worked into five hands-on labs. Toggle, build, guess, and check — the ideas stick better when your hands do them.
Person k toggles every k-th locker. Run all 100 people through, one at a time, or jump straight to the end. Watch which lockers survive open — and why.
Every square is a stack of consecutive odd numbers. Drag the slider and watch the L-shaped layers get added, one odd number at a time.
A cube of side n is n layers, each a square of n × n unit cubes. Slide n and watch the tower grow — layer by layer, exactly n³ little cubes.
Pick any number. Guess its square root by narrowing between the nearest perfect squares — the same "halve the interval" trick from page 9.
Type a number to see its prime factorisation, and whether the factors split into two identical groups (square) or three (cube).