One of the most popular features in the journal Mathematics Teacher, published by the Na...

One of the most popular features in the journal Mathematics Teacher, published by the National Council of Teachers of Mathematics, is the monthly calendar. It provides an interesting, unusual, or challenging problem for each day of the month. Some of these exercises, and others later in this text, are chosen from these calendars (the day, month, and year of publication of each problem are indicated). The authors want to thank the many contributors for permission to use these problems.

Use the various problem-solving strategies to solve each problem. In many cases there is more than one possible approach, so be creative.

How Much Is That Doggie in the Window? A man wishes to sell a puppy for $11. A customer who wants to buy it has only foreign currency. The exchange rate for the foreign currency is as follows: 11 round coins = $15, 11 square coins = $16, 11 triangular coins = $17. How many of each coin should the customer pay? (April 20, 2008)