If A and B are two events such that P(A) =0.2 ,P(B)= 0.4 and P(A ∪ B) = 0.5 then value of P(A/ B ) is :

0.25

Given: $P(A) = 0.2$, $P(B) = 0.4$, $P(A \cup B) = 0.5$

Use formula: $P(A \cup B) = P(A) + P(B) - P(A \cap B)$

$0.5 = 0.2 + 0.4 - P(A \cap B)$

$P(A \cap B) = 0.6 - 0.5 = 0.1$

Conditional probability: $P(A|B) = \frac{P(A \cap B)}{P(B)}$

$P(A|B) = \frac{0.1}{0.4} = 0.25$

Answer: $P(A|B) = 0.25$