Williams K.S., Hardy K. The Red Book of Mathematical Problems

Dover Publications, 2010. — 174 pages.Handy compilation of 100 practice problems, hints, and solutions indispensable for students preparing for the William Lowell Putnam and other mathematical competitions. Problems suggested by a variety of sources: Crux Mathematicorum, Mathematics Magazine, The American Mathematical Monthly and others. Preface to the First Edition. Sources. 1988 edition.