Chapter 13.5, Problem 20PPS

To determine

To derive formula for conditional probability.

Explanation of Solution

Let us take two dependent events.

P(A) and P(B)

Now we know that if the events A and B are dependent then,

P(A and B) = $\text{P(A)}\cdot \text{P(}\text{B}|\text{A)}$

  $\text{P(}\text{B}|\text{A)=}\frac{\text{P(A and B)}}{\text{P(A)}}$

Hence this is the required formula.