AHA! Puzzle This
By Michael H. Pryor
MAKE’s favorite puzzles. (When you’re ready to check your answers, visit makezine.com/13/aha.)
Radar Date
On October 2, 2001, the date in MM/DD/YYYY
format was a palindrome (the same forward as
backward): 10/02/2001.
When was the last date before 10/02/2001
that this phenomenon occurred?
Crystal Orbs
You have 2 identical crystal orbs. You need to figure
out at what height an orb can fall from a 100-story
building before it breaks. You know nothing about
the toughness of the orbs: they may be very fragile
and break when dropped from the first floor, or they
may be so tough that dropping them from the 100th
floor doesn’t even harm them.
What is the least number of orb drops you would
have to do in order to find the lowest floor they
break on? In other words, what’s the most efficient
way you could drop the orbs to find your answer?
You are allowed to break both orbs, provided that
in doing so you uniquely identify the correct floor.
Poison Pills
The evil king from an earlier MAKE puzzle sends
his own assassin to take care of the evil queen who
tried to poison him. Of course, her trusty guards
catch the assassin before any harm is done. The
queen notices that the assassin is quite handsome,
and she doesn’t really want to punish him with
death. She decides to test his wisdom.
The queen gives the assassin 12 pills that are all
completely identical in shape, smell, texture, and
size, but 1 pill has a different weight. The queen
gives the man a balance and tells him that all
the pills are deadly poison except for the pill of a
different weight. The assassin can make 3 weighings
and then must swallow the pill of his choice. If he lives,
he will be sent back to the bad king’s kingdom. If he
dies, well, that’s what he gets for being an assassin.
Only 1 pill is not poisonous, the one that has a
different weight. The assassin does not know if it
weighs more or less than the other pills.
How can he save his skin?
Michael Pryor is the co-founder and president of Fog Creek Software. He runs a technical interview site at techinterview.org.
Illustrations by Roy Doty
142 Make: Volume 13
