AHA! Puzzle This
By Michael H. Pryor
MAKE’s favorite puzzles. (When you’re ready to check your answers, visit makezine.com/14/aha.)
A dysfunctional family has to cross the river. On one
side of the river are the mom and 2 daughters, dad
and 2 sons, the maid, and the dog. There is a boat
only big enough to hold 2 people (counting the dog
as 1 person). Only the adults (mom, dad, maid) are
capable of operating the boat. Everyone has to get
to the other side, without anything bad happening.
There are some difficulties. If the dog is left with
anyone and the maid isn’t there to control him, he’ll
bite. The dad can’t stay with any of the daughters
when the mom isn’t there, or they’ll get into an
argument. Likewise, the mom can’t be alone with
either of the sons when the father isn’t there.
Remember, only an adult can operate the boat
(and it can’t drive itself). How do they cross?
An obsessive-compulsive ant starts at the
top left-hand corner of a square, checkered
tablecloth. He’s trying to reach the bottom
right corner with the cheesecake in it. He will
only move at right angles following the grid
lines of the tablecloth. Also, he will only move
toward the cheesecake (in other words, down
or to the right, never up or to the left).
If the tablecloth is a 2× 2 square, the ant has
6 distinct paths he can take (see illustration).
How many paths are there if he’s on an 8× 8
Illustrations by Roy Doty
Michael Pryor is the co-founder and president of Fog Creek Software. He runs a technical interview site at techinterview.org.
174 Make: Volume 14