What is the probability that the roots of the equation x² + x + n = 0 are real, where n ∈ ℕ and n < 4?

If A and B are two events such that P(not A) = $\rm \frac{7}{10}$, P(not B) = $\rm \frac{3}{10}$ and P(A|B) = $\rm \frac{3}{14}$, then what is P(B|A) equal to?

Seven white balls and three black balls are randomly placed in a row. What is the probability that no two black balls are placed adjacently?

Let two events A and B be such that P(A) = L and P(B) = M. Which one of the following is correct?