Question

which one correctly notates the probability of event a given that event b already happened?
p(a / b)
p(b / a)
none of the above
p(a∩b)

Explanation:

The notation for the probability of event A given that event B has already occurred is the conditional probability notation \( P(A|B) \) (note: typically written with a vertical bar, not a slash, but the option here uses a slash which is likely a typo for the vertical bar). The other options: \( P(B|A) \) is the probability of B given A, and \( P(A \cap B) \) is the probability of both A and B occurring. So the first option, despite the slash (likely a typo for |), is the intended notation for A given B.

Answer:

A. \( P(A / B) \) (Note: This should be \( P(A|B) \) with a vertical bar, but the option uses a slash, likely a typo.)