An insurance company have offices in Chicago, Detroit and Milwaukee. An office is chosen at random, and 100 policyholders are selected at random from this office in order to perform an age analysis of its policyholders.
What the company doesn't realize is that the age distibution of policyholders is not the same in each office.
In the Chicago office, 28% of policyholders are under 30; in the Detroit office, 35% are under 30, abd in th Milwaukee office only 18% are under 30.
Given that in the sample of 100, 30 were under the age of 30, what is the probablilty that the Detroit office was chosen?

Thanks!!!!