we are given the probability of rain tomorrow of 60 % and a 40% chance of wind and rain. we are asked for the probability that it is windy, given that it is rainy. The formula that should be used is the quotient of the probability with "and" over the probability of the rain only. Hence, P[W U R ] / P [R] = 0.4 / 0.6 = 2/3 = 67%
