“What does a mathematician do?” someone once asked the author, and from that simple inquiry sprang this entertaining and informative volume. Designed to explain and demonstrate mathematical phenomena through the use of photographs and diagrams, Dr. Steinhaus’s thought-provoking exposition ranges from simple puzzles and games to more advanced problems in mathematics. For this revised and enlarged edition, the author added material on such wide-ranging topics as the psychology of lottery players, the arrangement of chromosomes in a human cell, new and larger prime numbers, the fair division of a cake, how to find the shortest possible way to link a dozen locations by rail, and many other absorbing conundrums. This appealing volume reflects the author’s longstanding concern with demonstrating the practical and concrete applications of mathematics as well as its theoretical aspects. It not only clearly and convincingly answers the question asked of Dr. Steinhaus but also offers readers a fascinating glimpse into the world of numbers and their uses.