A Compensatory Harmonica

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A problem from the American Mathematical Monthly, March 1930:

Two men jointly own x cows. They sell these for x dollars per head and use the proceeds to buy some sheep at $12 per head. Their income from the cows isn’t divisible by 12, so they buy a lamb with the remainder. Later they divide the flock so that each man has the same number of animals. This leaves the man with the lamb somewhat short-changed, so the other man gives him a harmonica. What’s the harmonica worth?

Click for Answer

Podcast Episode 135: Lateral Thinking Puzzles

http://commons.wikimedia.org/wiki/Category:Thinking#mediaviewer/File:Mono_pensador.jpg

Here are six new lateral thinking puzzles to test your wits and stump your friends — play along with us as we try to untangle some perplexing situations using yes-or-no questions.

Below are the sources for this week’s puzzles. In a few places we’ve included links to further information — these contain spoilers, so don’t click until you’ve listened to the episode:

Puzzle #1 was devised by Sharon. Here’s some more information.

Puzzle #2 was contributed by listener Jon Sweitzer-Lamme, who sent these corroborating links.

Puzzle #3 is from listener Jonathan Knoell.

Puzzle #4 is from listener Nick Hare.

Puzzle #5 is from Paul Sloane and Des MacHale’s 2014 book Remarkable Lateral Thinking Puzzles.

Puzzle #6 was devised by Greg. Here’s a link.

You can listen using the player above, download this episode directly, or subscribe on iTunes or Google Play Music or via the RSS feed at http://feedpress.me/futilitycloset.

Please consider becoming a patron of Futility Closet — on our Patreon page you can pledge any amount per episode, and we’ve set up some rewards to help thank you for your support. You can also make a one-time donation on the Support Us page of the Futility Closet website.

If you have any questions or comments you can reach us at podcast@futilitycloset.com. Thanks for listening!

Graft

graft puzzle

You’re a venal king who’s considering bribes from two different courtiers.

Courtier A gives you an infinite number of envelopes. The first envelope contains 1 dollar, the second contains 2 dollars, the third contains 3, and so on: The nth envelope contains n dollars.

Courtier B also gives you an infinite number of envelopes. The first envelope contains 2 dollars, the second contains 4 dollars, the third contains 6, and so on: The nth envelope contains 2n dollars.

Now, who’s been more generous? Courtier B argues that he’s given you twice as much as A — after all, for any n, B’s nth envelope contains twice as much money as A’s.

But Courtier A argues that he’s given you twice as much as B — A’s offerings include a gift of every integer size, but the odd dollar amounts are missing from B’s.

So who has given you more money?

The Two Errand Boys

dudeney errand boys

Another conundrum from Henry Dudeney’s Canterbury Puzzles:

A country baker sent off his boy with a message to the butcher in the next village, and at the same time the butcher sent his boy to the baker. One ran faster than the other, and they were seen to pass at a spot 720 yards from the baker’s shop. Each stopped ten minutes at his destination and then started on the return journey, when it was found that they passed each other at a spot 400 yards from the butcher’s. How far apart are the two tradesmen’s shops? Of course each boy went at a uniform pace throughout.

Click for Answer

Growth Potential

Suppose you’re working on an algebraic expression that involves variables, addition, multiplication, and parentheses. You try repeatedly to expand it using the distributive law. How do you know that the expression won’t continue to expand forever?

For example, expanding

(x + y)(s(u + v) + t)

gives

x(s(u + v) + t) + y(s(u + v) + t),

which has more parentheses than the original expression.

Click for Answer

Black and White

hochberg puzzle

To kill some time before a meeting of chess grandmasters, Burt Hochberg offered this anonymous puzzle from the 15th century. White must place four white rooks on the board, one at a time, giving check with each one. After each placement the black king can respond with any normal legal move. How can White plan his moves so that the fourth rook reliably gives checkmate?

There’s no trick, and in fact there are several solutions, but Hochberg says the grandmasters studied the position for several minutes before Paul Keres came up with an answer. What was it?

Click for Answer

8 Is Enough

8 Is Enough - problem

This is said to have been the most popular problem presented in the American Mathematical Monthly. It was proposed by P.L. Chessin of Westinghouse in the April 1954 issue. Each of the digits in this long division problem has been replaced with an x — except for a single 8 in the quotient. Can you reconstruct the problem?

Click for Answer

The Squire’s Puzzle

dudeney squire puzzle

Another conundrum from Henry Dudeney’s The Canterbury Puzzles:

A squire has drawn a portrait of King Edward III with a single continuous stroke of his pen. “‘Tis a riddle to find where the stroke doth begin and where it doth also end. To him who shall first show it unto me will I give the portraiture.” What is the answer?

Click for Answer

The Cornish Cliff Mystery

dudeney cliff puzzle

Police have chased two thieves to the Cornish coast. There they find that two sets of footprints depart the hard road and cross soft soil to the edge of a cliff, where they end. The cliff juts out 200 feet above sea-washed boulders. No one could survive a fall from this height, there is no way to descend the cliff, and there are no other footprints.

The police have proven that the footprints match those of the fleeing criminals. The small foot belongs to Marsh, who apparently takes relatively long strides, walking heavily on his heels. Lamson takes shorter strides, treading more on his toes and evidently following behind Marsh, as he sometimes treads over the smaller man’s footprints.

The two men did not walk to the cliff edge and then return to the road by walking backward in their own footprints — such precision over a course of 200 yards is impossible. Accordingly the inspector says he will report that the criminals, hopeless to escape justice, have hurled themselves to their death.

“Then you will make a fatal mistake,” says Henry Melville, a visiting member of the Puzzle Club. “The men are alive and in hiding in the district.” He proves to be right, but how did the men get away from the edge of the cliff?

Click for Answer

Mens et Manus

http://cs.nyu.edu/~gottlieb/tr/back-issues/2000s/2008/2-mar-apr-tr.pdf

David Hagen offered this puzzle in MIT Technology Review in 2007. The MIT logo can be thought of as a slider puzzle. In the figure above, can you slide the tiles about so that the gray I can escape through the opening at top left?

Click for Answer