Well Done

http://commons.wikimedia.org/wiki/File:Filippo_Palazzi_-_Giovinetta_alla_sorgente_(Napoli).jpg

Using a 7-quart and a 3-quart jug, how can you obtain exactly 5 quarts of water from a well?

That’s a water-fetching puzzle, a familiar task in puzzle books. Most such problems can be solved fairly easily using intuition or trial and error, but in Scripta Mathematica, March 1948, H.D. Grossman describes an ingenious way to generate a solution geometrically.

Let a and b be the sizes of the jugs, in quarts, and c be the number of quarts that we’re seeking. Here, a = 7, b = 3, and c = 5. (a and b must be positive integers, relatively prime, where a is greater than b and their sum is greater than c; otherwise the problem is unsolvable, trivial, or can be reduced to smaller integers.)

Using a field of lattice points (or an actual pegboard), let O be the point (0, 0) and P be the point (b, a) (here, 3, 7). Connect these with OP. Then draw a zigzag line Z to the right of OP, connecting lattice points and staying as close as possible to OP. Now “It may be proved that the horizontal distances from OP to the lattice-points on Z (except O and P) are in some order without repetition 1, 2, 3, …, a + b – 1, if we count each horizontal lattice-unit as the distance a.” In this example, if we take the distance between any two neighboring lattice points as 7, then each of the points on the zigzag line Z will be some unique integer distance horizontally from the diagonal line OP. Find the one whose distance is c (here, 5), the number of quarts that we want to retrieve.

Now we have a map showing how to conduct our pourings. Starting from O and following the zigzag line to C:

  • Each horizontal unit means “Pour the contents of the a-quart jug, if any, into the b-quart jug; then fill the a-quart jug from the well.”
  • Each vertical unit means “Fill the b-quart jug from the a-quart jug; then empty the b-quart jug.”

So, in our example, the map instructs us to:

  • Fill the 7-quart jug.
  • Fill the 3-quart jug twice from the 7-quart jug, each time emptying its contents into the well. This leaves 1 quart in the 7-quart jug.
  • Pour this 1 quart into the 3-quart jug and fill the 7-quart jug again from the well.
  • Fill the remainder of the 3-quart jug (2 quarts) from the 7-quart jug and empty the 3-quart jug. This leaves 5 quarts in the 7-quart jug, which was our goal.

You can find an alternate solution by drawing a second zigzag line to the left of OP. In reading this solution, we swap the roles of a and b given above, so the map tells us to fill the 3-quart jug three times successively and empty it each time into the 7-quart jug (leaving 2 quarts in the 3-quart jug the final time), then empty the 7-quart jug, transfer the remaining 2 quarts to it, and add a final 3 quarts. “There are always exactly two solutions which are in a sense complementary to each other.”

Grossman gives a rigorous algebraic solution in “A Generalization of the Water-Fetching Puzzle,” American Mathematical Monthly 47:6 (June-July 1940), 374-375.

| Puzzles · Science & Math

A Magic Mystery

collison bimagic square

In 1991, David Collison sent this figure to Canadian magic-square expert John Henricks, with no explanation, and then died.

It’s believed to be the first odd-ordered bimagic square ever discovered. Each row, column, and diagonal produces a sum of 369. The square remains magic if each number is squared, with a magic sum of 20,049.

No one knows how Collison created it.

UPDATE: Wait, Collison’s wasn’t the first — G. Pfeffermann published a 9th-order bimagic square as a puzzle in Les Tablettes du Chercheur in 1891. (Thanks, Baz.)

| Science & Math

Regrets

On June 28, 2009, Stephen Hawking hosted a party for time travelers, but he sent out the invitations only afterward.

No one turned up.

He offered this as experimental evidence that time travel is not possible.

“I sat there a long time,” he said, “but no one came.”

| Science & Math

Misc

  • To frustrate eavesdroppers, Herbert Hoover and his wife used to converse in Chinese.
  • Asteroids 30439, 30440, 30441, and 30444 are named Moe, Larry, Curly, and Shemp.
  • COMMITTEES = COST ME TIME
  • 15618 = 1 + 56 – 1 × 8
  • How is it that time passes but space doesn’t?

Webster’s Third New International Dictionary gives no pronunciation for YHWH.

| History · Language · Religion · Science & Math

The Tippe Top

https://youtube.com/watch?v=xu_Dp9IfgSU%3Frel%3D0

The tippe top is a round top that, when spun, tilts to one side and leaps up onto its stem. This is perplexing, as the toy appears to be gaining energy — its center of mass rises with the flip.

How is this possible? The geometrical center of the top is higher than its center of mass. As the toy begins to topple to one side, friction with the underlying surface produces a torque that kicks it up onto its stem. It does gain potential energy, but it loses kinetic energy — in fact, during the inversion it actually reverses its direction of rotation.

Entire treatises have been written on the underlying physics, and the toy has occupied at least two Nobel Prize winners — below, Wolfgang Pauli and Niels Bohr play with one at the inauguration of the Institute of Physics at Lund, Sweden, in July 1954.

http://en.wikiquote.org/wiki/File:Pauli_wolfgang_c4.jpg

| Science & Math

Constellation

German astronomer Karl Reinmuth discovered and named more than 400 asteroids. Among them are these eight:

1227 Geranium
1228 Scabiosa
1229 Tilia
1230 Riceia
1231 Auricula
1232 Cortusa
1233 Kobresia
1234 Elyna

Their initials spell G. STRACKE, for Gustav Stracke, a fellow astronomer who had asked that no planet be named after him. In this way Reinmuth could honor his colleague without contradicting his wish.

| Language · Science & Math

Shorthand

University of Michigan mathematician Norman Anning offered this “non-commutative soliloquy of an introspective epistemologist” in Scripta Mathematica in 1948:

[(N + H)ow + (T + W)hat](I know).

Expand the expression and you get Now I know how I know that I know what I know.

| Science & Math

Contraband

http://commons.wikimedia.org/wiki/File:Astronaut_John_Young_gemini_3.jpg

Astronaut John Young smuggled a corned beef sandwich into space. As Gemini 3 was circling Earth in March 1965, Young pulled the sandwich out of his pocket and offered it to Gus Grissom:

Grissom: What is it?

Young: Corned beef sandwich.

Grissom: Where did that come from?

Young: I brought it with me. Let’s see how it tastes. Smells, doesn’t it?

Grissom: Yes, it’s breaking up. I’m going to stick it in my pocket.

Young: Is it? It was a thought, anyway.

“Wally Schirra had the sandwich made up at a restaurant at Cocoa Beach a couple of days before, and I hid it in a pocket of my space suit,” Young explained later. “Gus had been bored by the official menus we’d practiced with in training, and it seemed like a fun idea at the time.”

Grissom wrote, “After the flight our superiors at NASA let us know in no uncertain terms that non-man-rated corned beef sandwiches were out for future space missions. But John’s deadpan offer of this strictly non-regulation goodie remains one of the highlights of our flight for me.”

| Science & Math

Misc

  • Colombia is the only South American country that borders both the Atlantic and the Pacific.
  • GRAVITATIONAL LENS = STELLAR NAVIGATION
  • 28671 = (2 / 8)-6 × 7 – 1
  • Can a man released from prison be called a freeee?
  • “Nature uses as little as possible of anything.” — Johannes Kepler

Sergei Prokofiev died on the same day that Joseph Stalin’s death was announced. Moscow was so thronged with mourners that three days passed before the composer’s body could be removed for a funeral service.

(Thanks, Alina.)

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