Question 5
The currency of a certain country consists of bills of denominations 1, 5, 10, 20, 50 and 100 dollars. One day, two customers came to John's confectionery shop. Each bought a box of chocolate which cost 15 dollars. The first customer had two 10-dollar bills and the second one a 20-dollar bill and a 5-dollar bill. Having no money in the tilt, John was unable to give change when the customer paid separately. However, the first customer could pay the second customer with his two 10-dollar bills and receive the 5-dollar bill as change, and then the second customer could pay John the 20-dollar bill and one 10-dollar bill for both boxes. On another day, two customers came, and each bought a box of caramel. Once again, the tilt was empty, and the correct change could only be made if the two customers paid together. Among the following prices, which could have been that of a box of caramel?