According to Bayes' formula: P(B/default) = P(default and B)/P(default)
P(default and B ) = P(default/B)×P(B) = 0.250×0.300 = 0.075
P(default and CCC) = P(default/CCC)×P(CCC) = 0.400×0.700 = 0.280
P(default) = P(default and B) P(default and CCC) = 0.355
P(B/default) = P(default and B)/P(default) = 0.075/0.355 = 0.211
没有看懂