### Solution to Assignment #2

Please refer to Assignment #2 for the puzzle stories and the questions.

The puzzle story for Problem 1, THE STRIPE ON BARBERPOLIA, is the seventh riddle in Martin Gardner's Riddles of the Sphinx. Here is his solution, slightly edited:

If you cut a right triangle out of paper, then roll it along its base to make a cylinder, you'll see that the hypotenuse will form a helix---a line that spirals around the cylinder from one end to the other.

Imagine that the cylinder ... has been produced in this way. In your mind, unwrap the triangle... The height of the right triangle corresponds to the cylinder's length. In this case, it is 14,400. Because the helical stripe goes seven times around the cylinder, the unwrapped triangle will have a base that is seven times the cylinder's circumference, or 7 * 8,100 = 56,700 km.

The helical stripe corresponds to the triangle's hypotenuse. Its square must equal the sum of the squares of the other two sides. The square of 14,400 is 207,360,000, and the square of 56,700 is 3,214,890,000. The sum [of these] is 3,422,250,000. A punch of your calculator's square root key gives the square root of this number as 58,500. This is the length in kilometers of the helical stripe.

As for Problems 2 and 3, EXCELSIOR is the first "Knot" of Lewis Carroll's A Tangled Tale, which was originally a magazine serial. You can find it online; there's a link from Stefan's home page. Here are Carroll's own solutions:

Problem.---"Two travelers spend from 3 o'clock till 9 in walking along a level road, up a hill, and home again: their pace on the level being 4 miles an hour, up hill 3, and down hill 6. Find distance walked: also (within half an hour) time of reaching top of hill."