Let P(A) be the probability of a certain person buying a shirt.
∴ P(A) = 0.2
Let P(B) be the probability of him buying a coat.
∴ P(B) = 0.3
Let P(A ∩ B) be the probability that he buys both a shirt and a coat.
Tip – By conditional probability, P(A/B) = \(\frac{P(A \cap B)}{P(B )}\) where P(A/B) is the probability of occurrence of the event
A given that B has already occurred.
The probability that he will buy a shirt given that he buys a coat:
⇨ P(A∩B) = P(B) P(A⁄B)
= 0.3 × 0.4
= 0.12
