1. The problem statement, all variables and given/known data A survey concludes that it in average rains 15 of 30 days in may. Thusly P(R|M) = 1/2 Where M is May and R is rain. The Weatherservice forcasts fits 2/3 of the time. Thus it does not rain 2/3 of the time. I bring umbrella with me every day the promise and 1/3 of the days where do not perdict rain. 1) What is the prob that that Weather Service promises dry weather in a day in May? 2) What is the prob that it rains on a day where I did not bring my umbrella? 2. Relevant equations P(A|B) = P(A n B)/P(B) 3. The attempt at a solution By using the formula in condition prob. I get 1) P(R|M) = 1/2 P(R) = P(R) = 1 - P(does not rain) = 1 - 1/3 = 2/3 Thus 1/2 = P(R n M) / P(R) -> 1/2 = (R n M)/ (2/3) = 1/3 I am not sure about 2 ? 2) P = 1/3 * 2/3 = 2/9 ? Hope there is someone who would take a look at it?