Ebook: The Stanford Mathematics Problem Book: With Hints and Solutions (Dover Books on Mathematics)

This is an interesting little book for anyone who wants to bend their brain up for a little diversion or just for fun. This book is based on a test that was given to high school students to award the best a chance at a scholarship to college. This is the complete battery of problems that was given (I think minus one or two years that could not be found) to high school students in several schools. Although the problems are "high school level", it is immediately obvious that the level of problems given during this testing was a little more advanced from what is today perceived as high school mathematics.

Very enjoyable book for stretching your mind.