“Once I was in Moscow, buying an antique Russian gun for my collection. One kindly antiques trader offered me a cup of tea and some gingerbread. When he heard of my passion for brain twisters he told me a riddle that had been posed by one of the great Russian writers. I knew the answer at once. What about you?”

“A hat is on sale in a store for 10 rubles. A customer tries it on and wants to buy it but he only has a 25-ruble bill. The salesman sends his assistant next door to get change and he returns with two 10-ruble bills and one 5-ruble bill. The salesman gives the customer the hat and 15 rubles change. Later the neighbor calls in and says that the 25-ruble bill is a forgery and demands her money back. The salesman has no choice but to take the money from the cash register and give it back to her. The question is, what was the salesman’s loss?”