Dr. Ecco's Cyberpuzzles: 36 Puzzles for Hackers and Other Mathematical Detectives, by Dennis Elliott Shasha
The puzzles collected here require no formal background beyond arithmetic and elementary algebra.just lively curiosity and keen intelligence. With 36 illustrated cases organized around eight major mathematical themes (from "Combinatorial Geometry and Geography" to "Ciphers and Secrecy"), this book will encourage you to use your mind and your computer in ways you never previously imagined.

There are 9 gold coins. They all weigh the same except one is lighter than the others. Find this coin with two weighings on a pan balance. Answer

	    S E N D
	  + M O R E
	  ---------
	= M O N E Y

The symbols S, E, N, D, M, O, R, and Y represent different digits, which must be deduced. Answer

A snail is at the bottom of a 20 meters deep pit. Each day the snail climbs 5 meters upwards, but at night it slides 4 meters back downwards. How many days does it take the snail to reaches the top of the pit? Answer

Two cars are 120 miles from each other on a straight road. They drive towards each other at 30 mph (relative to the road). At the instant they set off, a bird leaves one car, flying towards the other at 60 mph. When it reaches the second car it turns back to the first car, and continues flying back-and-forth till the cars pass each other. When the cars pass, how far has the bird flown? (Total distance, not 'how far from starting point.) Answer

What is one-half of two-thirds of three-quarters of four-fifths of five-sixths of six-sevenths of seven-eights of eight-ninths of nine-tenths of one hundred? Answer