_AHA! Puzzle This By Michael H. Pryor

MAKE’s favorite puzzles. (When you’re ready to check your answers, visit makezine.com/11/aha.)

start at the back of the line and ask each gnome to guess the color of his own hat. Each gnome can only answer either “red” or “blue.” If he gives the wrong answer, he will be led off to work on the wizard’s landscaping for the rest of eternity. If he answers correctly, he will be returned to his own garden. Then the wizard will move on to the next gnome in line.

All of the gnomes will be able to hear the answers of the gnomes behind them, but they will not know if they were led off to forced labor or if they answered correctly and were set free. The gnomes are allowed to consult and agree on a strategy beforehand (while the wizard listens in) but after being lined up, they will not be able to communicate in any other way besides their answer of “red” or “blue” (in other words, they

Point of Gnome Return won’t be able to change the pitch of their voice or One hundred very smart garden gnomes are give any other clues to the other gnomes once they snatched from their homes by an evil wizard. He are in line and the hats are placed on their heads). tells them he is going to line them all up in a row, and What strategy should the gnomes use to maximize place a red or blue hat on each of their heads. They the total number of gnomes that will be set free? won’t be able to see the color of their own hats or Hint: They can do pretty well, even if the wizard hears anyone’s behind them, but they will be able to see the their plan and puts the hats on in such a way to hats of the gnomes in front of them. The wizard will thwart whatever idea they come up with.

Human Race

Illustrations by Roy Doty

Five makers (Ben, Mark, Jason, Ruth, and Joel) raced in an extravaganza for alternative transportation. They competed in five separate races: a Segway race, a bicycle race, a hybrid car race, a skateboard race, and a roller skate race. Points were given as follows: 5 points for first place, 4 points for second, 3 points for third, 2 points for fourth, and 1 point for last place. Overall scores were determined by adding up the individual scores from each race.

Ben got the highest number of points: 24. Jason finished in the same place in four out of the five races. Joel came in first in the skateboard race, and third in the roller skate race.

The final total rankings for the races were: Ben, Mark, Jason, Ruth, and then Joel. There were no ties

in any individual races, and no two racers had the same total score.

What place did Mark come in during the skateboard race?

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

Make: 181