The areas of 10 cities are given in the table. How much greater is the range for the cities in the south than the cities in the north?

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mi²

Northern Cities Southern Cities
Chicago 234 mi² Houston 627 mi²
Milwaukee 97 mi² New Orleans 350 mi²
Madison 85 mi² Phoenix 517 mi²
Detroit 143 mi² Memphis 324 mi²
Minneapolis 58 mi² Atlanta 132 mi²

Aprisoner 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 probabili- ties 0.5,0.3,0.2 (respectively), what is the expected number of days until he reaches freedom? (b) assuming that the prisoner is always equally likely to choose among those doors that he has not used, what is the expected number of days until he reaches freedom? (in this version, if the prisoner initially tries door 1, for example, then when he returns to the cell, he will now select only from doors 2 and 3.) (c) for parts (a) and (b), find the variance of the number of days until the prisoner reaches freedom. hint for part (b): define ni to be the number of additional days the prisoner spends after initially choosing door i and returning to his cell.