Solution (source code)

= Solution

The <conditional probability> rescales the <probability> of the part of $A$ lying in $B$ by the <probability> of $B$:
$$
\boxed{\mathbb P(A\mid B)=\frac{\mathbb P(A\cap B)}{\mathbb P(B)},\qquad\mathbb P(B)>0.}
$$
The denominator makes $B$ itself have <conditional probability> one.