Some farm animals need to cross the river. The class picks planks to fill the gap exactly. If the bridge is too short, the animal falls in. If it's too long, it won't fit.
Planks
Game
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Teacher tips and shortcuts
Tap a plank in the pile to lay it across the gap. Tap a plank on the bridge to take it back. When the planks fill the gap, press Cross!.
The planks in the pile are drawn to scale, so a 1 is twice as long as a ½. With whole numbers they're the same size as on the bridge.
A bridge that's too short drops the animal in the river, and the board says by how much. A bridge that's too long sticks out over the bank and glows red.
Three ways across: the same planks in a different order don't count as a new way. At the end the game says how many ways there are in all.
Fewest planks: the pile is small. Taking the longest plank each time doesn't always give the fewest. Ask the class to check before crossing.
Turn off the measuring tape (T) when the class is ready to work it out without it.
Keyboard: 1–5 lay a plank, Backspace undo, Delete clear, Enter cross, N new gap, F full screen, M sound, Esc this menu.