_AHA! Puzzle This By Michael H. Pryor

MAKE’s favorite puzzles. (When you’re ready to check your answers, visit makezine.com/08/aha.)

Gold Chain

A man has a gold chain with seven links. He needs the service of a laborer for seven days at a fee of one gold link per day. However, each day of work needs to be paid for separately. In other words, the worker must be paid each day after working, and if the laborer is ever overpaid he will quit with the extra money. Also, he will never allow himself to be owed a link. The laborer will keep the links he is paid in his pocket until the end of the week.

What is the fewest number of cuts the man can make to the chain to allow the laborer to be paid?

Monty Hall Problem Monty Hall, host of the game show Let’s Make a Deal, presents you with three doors. One door has a million dollars behind it. The other two have goats behind them. You do not know ahead of time what is behind any of the doors, but Monty Hall d oes. Monty asks you to choose a door. You pick one of the doors and announce it to him. Monty then counters by showing you one of the doors with a goat behind it and asks you if you would like to keep the door you chose, or switch to the other unknown door. Should you switch your choice, and if so, why? What is the probability of finding the million dollars if you don’t switch? What is the probability if you do?

Illustrations by Roy Doty

Chicken Nuggets

You can go to a fast food restaurant to buy chicken nuggets in 6-packs, 9-packs, or 20-packs. Is there such a number N, so that for all numbers bigger than or equal to N, you can buy that exact number of chicken nuggets using 6, 9, and 20 packs?

Michael Pryor is the co-founder and president of Fog Creek Software. He runs a technical interview site at techinterview.org.

Make: 179