A building contains two elevators, one fast and one slow. The average waiting time for t...

A building contains two elevators, one fast and one slow. The average waiting time for the slow elevator is 3 min. and the average waiting time of the fast elevator is 1 min. If a passenger chooses the fast elevator with probability 2/ 3 and the slow elevator with probability 1/ 3 , what is the expected waiting time? (Use the law of total expectation, Theorem A of Section 4.4.1, defining appropriate random variables X and Y .)

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