AHA! Puzzle This
By Michael H. Pryor
MAKE’s favorite puzzles. (When you’re ready to check your answers, visit makezine.com/09/aha.)
A Matter of Degree
What is the angle
between the minute
hand and the hour hand
at 3: 15 on an analog
clock? (Hint: It’s not 0.)
How often does the
minute hand pass
the hour hand on an
analog clock?
Reptilian Repetition
At one point, a tropical island’s
population of chameleons was
divided as follows:
13 red chameleons
15 green chameleons
17 blue chameleons
Each time two different-colored chameleons would
meet, they would change their
color to the third one. For
example, if green meets red,
they both change their color
to blue. Is it ever possible for
all chameleons to become the
same color? Why or why not?
Illustrations by Roy Doty
100 Lockers
You have 100 lockers in a high school hallway that are all initially closed. You walk down the hallway 100
times starting at the first locker each time. The first time down the hallway, you go to every locker, and if it
is open you close it; if it is closed, you open it. The second time you walk down the hallway, you only visit every
second locker (lockers #2, #4, #6, etc), reversing the state of each locker you visit. The third time through,
you visit every third locker (lockers #3, #6, #9, etc). You continue this until your 100th pass down the hallway when you only visit locker #100. When you are finished, which lockers are open and which are closed?
Michael Pryor is the co-founder and president of Fog Creek Software. He runs a technical interview site at techinterview.org.
Make: 189
