Assignment:
In a local town, there are three separate apartment blocks, A, B and C. Block A contains 10 apartments, of which two contain "High Risk" inhabitants. Block B contains eight apartments, with three occupied by "High Risk" inhabitants, and Block C contains 12 apartments, with four "High Risk" apartments.
Assume that an apartment in Block B was visited, and found to be a "High Risk" apartment. If the Fire Brigade now wishes to visit another apartment, again to be selected at random from all three blocks, what is the probability that the second flat will not be "High Risk"?
Provide complete and step by step solution for the question and show calculations and use formulas.