Solution to Challenge 3

Predicting the floor
The planning script gives side / 3. For 18 cm paper: 18 / 3 = 6.0 cm, so predict a floor of about 6 cm.

Folding and measuring
1. Fold the box from an 18 cm square and measure the inside floor along one edge.
2. Expect a result close to 6 cm, perhaps a few millimetres either way, depending on the paper's thickness and how tightly the flaps are tucked.

Wet-folding comparison
1. Fold a second box from watercolour paper.
2. Dampen the walls very lightly with a sponge and press them gently into shape, then leave it to dry.
3. The wet-folded box has softer, slightly rounded walls and holds its shape well once dry. The dry-folded box has sharp edges and crisp corners.

Checkpoint: your measured floor is within about half a centimetre of the prediction, and you can describe one visible difference between the two boxes. If the watercolour box tore or wrinkled, use less water next time.