"The Mathematician's Delight", a paperback by W.W. Sawer, first published Aug.1,1943 was an excellent publication I read at an early age and it was _extremely_ well written.
From the simple fundamental principles of mathemathics all the way to Calculus and Probability; without the incomprehensible intellectual tripe that most books on mathematics contain.
It is a highly recommendable read even for the non-mathematically inclined; you will certainly be enlightened as to 'how, why and what for', whether you have zero knowledge or a degree in mathematics to start with.
This is a book of facts written in the style of a good novel where the story of mathematics unfolds in digestable measures for any age-group, young or old.