The Thursday Packet (two printable pages). Page one is the fair ledger: Bread 240, Cakes 3, Pies 150, Total 393. Page two is a drawing of the open cash box: six pound coins, one fifty-pence piece and two twenty-pence pieces.

Try it before chapter 5. Count the cash box. Does it match the total? Before you decide anyone took money, ask what unit each line is in.

The answer. The cash box holds £6.90. The cakes line means three pounds, so in pennies the fair made 240 + 300 + 150 = 690, which is £6.90. Nothing is missing; the ledger mixed pennies and pounds.

No printer? Write the three lines on a card, and use real coins for the cash box.

The grown-up layer. A number without its unit is the most common source of "wrong" answers that were right all along. Adding in a different order is a quick, honest check. The story also refuses to blame anyone before the sum is checked. ReckonQuest teaches drawing a bar, tracking units and looking back.

For the ride home. Ask: what would have happened if Inkling had been believed?