The Arithmetic of Maybe

What this book is about

Most of the questions that really matter do not have "yes" or "no" for an answer. Will it rain tomorrow? Will the medicine work? Will this seed give a good harvest? Is the number in that report true? The honest answer to all of them is the same — maybe. This book teaches you to write that "maybe" as a number.

In school, probability is usually taught by memorising formulas. So plenty of students can write nCr and still have no idea what the newspaper means by "leading with 52% in the poll". This book walks the other way round: first the situation, then the numbers, and only at the end the formula. Nothing falls out of the sky — every rule is built on the page where it first appears.

The cover says "for young readers". The truth is that this book's most important reader may be a grown-up who never understood this at school — and who concluded the fault was theirs. It was not.

What is inside

• What a probability actually is, why it never leaves 0 and 1, and why a coin has no memory
• "And" or "or", conditional probability, trees, and counting the arrangements
• Mean, standard deviation, and the several honest ways a graph can lie
• The bell curve, 68 · 95 · 99.7, and z-scores for comparing two different exams
• Sampling, margin of error, Bayes, and the mistake courtrooms keep making
• The people who built it — Pascal and Fermat on dice, the *meru-prastāra* of this

subcontinent, Bernoulli, Nightingale and Mahalanobis

• Two experiments to try, a formula sheet, worked exercises, a glossary and a quiz