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**Vinod** The various arrangements of discharging the passengers to any one floor may be denoted by symbols like (3,1,1) to be interpreted as the event that three passengers leave together at a certain floor, one passenger at another floor and finally the last one passenger at still another floor. So there are seven possible arrangements ranging from (5) to (1,1,1,1,1). Now calculate the total probability by adding probability for each arrangement. E.g. In how many ways all the five passengers gets off at any one floor. The answer is in $\binom{8}{1}$ ways. That is the way i calculated the answer $\frac{6720}{9192}$