A prisoner is trapped in a cell containing three doors. The first door leads to a tunnel that returns him to his cell after two days of travel. The second leads to a tunnel that returns him to his cell after three days of travel. The third door leads immediately to freedom. (a) Assuming that the prisoner will always select doors 1, 2 and 3 with probabilities 0.5, 0.3, 0.2 (respectively), what is the expected number of days until he reaches freedom