The Puzzler

Be thankful you already have a job.

Job interviews at many large companies feature brainteasers and puzzles that test the problem-solving skills of an applicant. When a job is on the line, these puzzles can be downright torturous, but absent that pressure, they can be quite a bit of fun.

Each month, the puzzle page will offer a real-world puzzle and its solution. The page will also feature a separate puzzle contest; the solution will be published the following month. The most elegant and original response to the second puzzle will receive a free copy of Kador's career book, How to Ace the Brainteaser Job Interview (McGraw-Hill, 2004). Please submit your solutions to [email protected], using the subject line, “November 2005 Puzzler.”

Real-World Puzzle #1

An advisor is looking for a promotion. One day, she says to her manager, “I can improve my performance by 1 percent per day. Every day, I'll do 1 percent more business than I did the day before.”

Should a manager be impressed with this promise? How long will it take for the advisor to double her performance? In other words, how long will it take for her to be twice as effective as she is today?

Solution

The advisor will double her performance in approximately 70 days (69.66 days to be exact). There are a couple of ways to solve this problem. The Rule of 70 is useful for financial, as well as demographic, analysis. The Rule of 70 states that to find the doubling time of a quantity growing at a given annual percentage rate, divide the percentage number into 70 to obtain the approximate number of years required to double. For example, at a 10 percent annual growth rate, doubling time is 70 / 10 = 7 years.

The accompanying table shows some common doubling times.

As you can see, for a 1 percent per-year increase, the doubling time would be 70 / 1 or 70 years. Not very impressive. But the advisor's promise is considerably bolder. She promises a 1 percent increase per day. So the answer must be expressed in days, or approximately 70 days.

Puzzle #2: Contest of the Month

If you had to eliminate one of the 50 U.S. states, which one would you select and why? On what basis did you make your selection?

Please email your solution to [email protected] by Nov. 25, 2005. The submission should include your name, address, affiliation and email. No purchase required. Only one submission per reader, please. We will publish the solution we consider the most original and elegant in this space next month. Good luck.

Complete Puzzle Rules

• The submission should include your name, address, affiliation and email address. No purchase required.

• Entries must be received by Nov. 25, 2005. One entry per person. Employees of Registered Rep. magazine and its affiliated publications are ineligible. Void where prohibited or restricted by law. Registered Rep. is not responsible for incomplete, lost, stolen, illegible, misdirected or late entries.

• One winner will be selected on the basis of accuracy, originality and elegance, as judged by the magazine staff. In some cases, the winner will be selected in a random drawing from all eligible entries that contain a correct answer to the month's puzzle. The decision of the judges is final. We will notify the winner by email.

• The winner will get his or her solution published in Registered Rep. The winner will also receive a copy of How to Ace the Brainteaser Job Interview inscribed by the author.

• All entries become the property of Registered Rep. Each contest entrant consents to the publication of his or her name and puzzle answer, in any and all media and manner, now or hereafter known, in perpetuity without compensation. Registered Rep. is not responsible for any damages or losses relating to the puzzle or acceptance/use of any prize.

Writer's BIO: John Kador, the author of 10 books, published Charles Schwab: How One Company Beat Wall Street and Reinvented the Brokerage Industry in 2003. His Web site is www.jkador.com