Question

According to the general equation for conditional probability, if P(AB)= 3/10 and P(B) =2/5, what is ? P(A l B)?
1. 1/2
2. 2/5
3. 1/16
4. 3/4

Answer 1

The formula for conditional probablity states that

$P(A | B) = \cfrac{P(A \cap B)}{P(B)}$

Since we know both numerator and denominator, we only need to plug in the values:

$P(A | B) = \cfrac{P(A \cap B)}{P(B)} = \cfrac{\frac{3}{10}}{\frac{2}{5}} = \cfrac{3}{10}\cdot\cfrac{5}{2} = \cfrac{3}{4}$