The Thursday Packet (two printable pages). Page one is the museum's test card, with three lines to fill in: the claim in one sentence, the line chosen before testing, and the result. Page two shows two coins on scales with measuring jugs. The known silver coin reads 31.5 grams and raises the water 3 cubic centimetres. The collector's coin reads 27 grams and also raises it 3.

Try it before chapter 5. Fill in the claim and the line first. Then work out grams per cubic centimetre for each coin.

The answer. The known coin is 31.5 ÷ 3 = 10.5. The collector's coin is 27 ÷ 3 = 9. Nine is under the line of ten, so the coin is not silver all the way through.

No printer? Write the three lines on a card. You can try the water test at home with a measuring jug and two stones.

The grown-up layer. Choosing the test before seeing the result is the heart of honest checking, in science and in everyday claims. Comparing with something known shows that the method works. TruthQuest is built on the same moves. Nobody in the story is fooled or blamed: the collector had simply been told the wrong thing.

For the ride home. Ask: why did Prove want the line written down before the coin was weighed?