All courses › Foundations of Mathematics › Probability

Probability

When all outcomes are equally likely, the probability is the number of favourable outcomes divided by the number of possible outcomes. For independent events the probabilities multiply, and the probability that something does not happen is one minus the probability that it does.

P(A) = \frac{g}{m}

favourable over possible

P(A\cap B) = P(A)\,P(B)

independent events

P(\bar A) = 1 - P(A)

the complement

Symbols

$P(A)$	probability of A
$g$	number of favourable outcomes
$m$	number of possible outcomes

Example

At least one six in two throws of a die:

$1 - (5/6)^2 = 11/36 \approx 0.31$ .

"At least one" is almost always easiest with the complement.

Practise statistics and probability for free →

← Standard deviation

Part of Foundations of Mathematics: Statistics and probability.