# What is Bayes' rule?

P(${B}_{i}$ /A) = P (${B}_{i}$ )P(A/${B}_{i}$ )/ $\sum$ P (${B}_{i}$ )P(A/${B}_{i}$ ) , where ${B}_{i}$ is the ith cause and A is the effect.
$\bigcup$ ${B}_{i}$ = S, ${B}_{i}$ $\bigcap$ ${B}_{j}$ = $\phi$ , ${B}_{i}$, i = 1, 2, ... k are the mutually exclusive and collectively exhaustive reasons under which the effect A takes place.