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The Pastry Shop Purchase Ledger (illustration)
FILE No.22Unsolved

The Pastry Shop Purchase Ledger

Difficulty ★★☆about 5 minTheft CasesCombinationsImpossible numbers
Goods are being diverted from a pastry shop. In four purchasers’ ledgers, one total count could never be made up from the boxes.

Case Record

A pastry shop’s stock does not add up. The manager suspects someone diverted goods and rewrote the total in the purchase ledger to hide it.

The supplier only handles the box types listed in the catalog in the scene diagram. Boxes cannot be opened to adjust the count.

The four buyers’ ledgers record these totals:

  • Kitamura: 38 pieces
  • Nakanishi: 41 pieces
  • Suzuki: 43 pieces
  • Hashimoto: 46 pieces

Checking against the delivery slips shows that exactly one person has written a total that cannot be made from the boxes.

Your question

Whose ledger has been rewritten? Look closely at the scene diagram and the evidence.

Case Files

Evidence

Supplier catalog

Supplier catalog

Timeline

  1. The manager notices the stock count is off.
  2. One ledger total cannot be made from the boxes.

Hints

If you get stuck, open the hints one at a time, in order.

Open hint 1

In the scene diagram, compare the contents of the 6-piece and 9-piece boxes.

Open hint 2

Subtract the number of 20-piece boxes on the delivery slip from each total.

Open hint 3

Can the remainder be made from 6- and 9-piece boxes?

Solve It

Your question

Whose ledger has been rewritten? Look closely at the scene diagram and the evidence.

Choose the answer closest to the truth.

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The Truth

Suzuki (43)

The answer is: Suzuki.

In the scene diagram, the 6-piece box is 2 small bags of 3 and the 9-piece box is 3 small bags of 3, so both are made of "bags of 3." Whatever you make from 6- and 9-piece boxes alone is always a multiple of 3.

Subtract the 20-piece boxes on the delivery slips from each total. Kitamura: 38 − 20 = 18. Nakanishi: 41 − 20 = 21. Hashimoto: 46 − 40 = 6. All are multiples of 3 (18 = 9 + 9, 21 = 9 + 6 + 6, 6 = 6).

But Suzuki: 43 − 20 = 23, which is not a multiple of 3. It cannot be made from 6- and 9-piece boxes, so only Suzuki’s ledger has been rewritten, to cover what was diverted.

What is left must be made of 6s and 9sBuyerTotal20-pc boxesLeftVerdictKitamura38118PossibleNakanishi41121PossibleSuzuki43123ImpossibleHashimoto4626Possible6s and 9s only make multiples of 3.
Diagram of the solution

Key Points

  • Read what the boxes have in common from the diagram
  • Subtract the 20-piece boxes and check the rest
  • Tell them apart by whether it is a multiple of 3

Why people get fooled

Every total looks plausible on its own. People pass them without reading what is inside the boxes.

Similar tricks

  • The type that spots an impossible number from how things are packed
  • The type that checks by subtracting a known part

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If you view the truth, this case will not count as solved on your own. Open it anyway?

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