The most difficult trade riddles

Registers typically use thermal printers to print receipts, although older dot matrix printers are still in use at some retailers. Thermo-sensitive coating used in thermal paper is sensitive to incidental heat, abrasion, friction (which can cause heat, thus darkening the paper), light (which can fade printed images), and water.

Situated 110 km (70 miles) from the North Sea on the river Elbe, the port of Hamburg is the second or third largest port in Europe (after the port of Rotterdam and Antwerp) and eleventh largest worldwide.

The stock price was 10 two days ago. Yesterday it dropped by 50% to 5. Today it raised by 50% (of 5) to 7.5