Explanation : The probability that at least one of the bonds will be called can be
calculated using the Addition rule of probability which is:
P(A or B) = P(A) + P(B) – P(A and B) where P(A and B)
is P(A) * P(B) P(A or B) = 0.6 + 0.5 - 0.6 * 0.5 = 0.8.