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## Frank Morgan's Math Chat |

November 15, 2001

**Old Challenge**. Is there any valid explanation for the Burger King sale:

Cheeseburger: $.49

Double Cheeseburger: $.99

Triple Cheeseburger: $1.49

(Why are three cheeseburgers cheaper than one triple cheeseburger, when the individual burgers have more bun but the same amount of meat?)

**Answer** (Arthur Pasternak). Sure, I can think of five explanations:

- It may be that it is very difficult to assemble a triple cheeseburger because it is hard to balance the tiny little things on top of each other. This difficulty could increase the overall cost of a triple cheeseburger, either because you need to hire more skilled (and higher paid) hamburger stackers to build them, or because it takes much longer. The additional cost may exceed the marginal cost of the additional buns.
- Double or triple burgers may not fit in the custom microwave burger heaters and therefore require special expensive burger heaters that cost substantially more. This cost is passed on to the customer.
- Perhaps the triples do cost a bit less, but Burger King makes a huge markup on other products in the $1.50 price range and wants to discourage people from buying the triple burgers.
- Triples require special high performance titanium buns which cost more.
- Marketing studies have shown that all prices need to end in the number 9 because customers are indifferent between $1.50 and $1.59. Therefore it makes sense to round all prices to the nearest number ending in 9.

Margaret Luck reports that at Kippax shops, Canberra Australia, you can buy one loaf of day-old bread for 80 cents, or three for $2.50, and they won't let you buy three loaves separately.

**Questionable Mathematics.** John Sullivan reports that the October 7 *New York Times* described some (evidently four-dimensional) rockets in use by the Afghan opposition, which "are designed to land in unison and pulverize a several-square-acre area." (Since acres are already two-dimensional units, a square acre must be a four-dimensional unit.)

Readers are invited to submit more examples of questionable mathematics.

**New Challenge** (Al Zimmermann). In the baseball World Series (best of 7), which should be more difficult: to come back from being behind 0-2, or to come back from being behind 2-3?

Copyright 2001, Frank Morgan.

Send answers, comments, and new questions by email to Frank.Morgan@williams.edu, to be eligible for* Flatland *and other book awards. Winning answers will appear in the next Math Chat. Math Chat appears on the first and third Thursdays of each month. Prof. Morgan's homepage is at www.williams.edu/Mathematics/fmorgan.

THE MATH CHAT BOOK, including a $1000 Math Chat Book QUEST, questions and answers, and a list of past challenge winners, is now available from the MAA (800-331-1622).