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
