50 Mathematical Ideas You Really Need To Know, by Tony Crilly.
ISBN 978-1-84724-147-4. This book as the title implies covers 50 mathematical ideas. It has a four page section for each idea. Each section is just a basic overview of the topic, but they are fun to read if you are interested in this subject. The only thing I would have liked to have seen was a reference section at the end that would point the reader to additional information about the various topics. On the other hand, the reader can easily look these topics up in wikipedia to get more info and further references. Some of the topics covered are zero, number systems (numeral systems), fractions, squares and square roots. Other subjects include pi, e, infinity, imaginary numbers, primes.