Probability · Basic probability
Chapter 1 · 3
The idea
Probability of a single event
Why a probability is a share of the whole — so it lives between 0 and 1, why P(A) = favourable ÷ total needs equally likely outcomes, and how the "it all adds to 1" rule drives complements, missing table entries and expected numbers.
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Probability · Basic probability
Probability of a single event
Why a probability is a share of the whole — so it lives between 0 and 1, why P(A) = favourable ÷ total needs equally likely outcomes, and how the "it all adds to 1" rule drives complements, missing table entries and expected numbers.
Why it works
A share of the whole, so the scale is 0 to 1
A probability is not a score out of ten and it is not a feeling. It is a share of the whole: picture everything that could happen as slices of one complete cake, and the probability of an event is how much of the cake it covers. Nothing can cover less than none or more than all of it, so every probability satisfies — impossible, certain. That makes the scale a free error-check: an answer of or is not a slightly wrong probability, it is not a probability at all.Keep reading — free
The rest of the explanation, plus 3 worked examples you step through move by move.
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