Answers 387the chapter on "The Calculus of Finite Differences" in my book New Mathe-
matical Diversionsfrom Scientific American.-M. G.]- AN EFFERVESCENT PUZZLE
The answer to the first case is 88,200 ways. There is an easy way of getting
the answer, but it would require too much space to explain it in detail. In the
second case the answer is reduced to 6,300 ways.
- TESSELLATED TILES
Discard the first tile in each of the four horiwntal rows. Then the remain-
ing sixteen may be arranged as shown in the illustration, in accordance with
the conditions.- THE THIRTY-SIX LETTER PUZZLE
If you have tried, as most people do, first to place all six of one letter, then
all six of another letter, and so on, you will find, after you have placed four
different kinds of letters six times each, it is impossible to place more than
two letters each of the last two letters, and you will get our arrangement