Five persons entered the lift cabin on the ground floor of an 8 floored house. Suppose that each of them independently and with equal probability can leave the cabin at any floor beginning with the first, then the probability of all 5 persons leaving at different floor is
As building has 8 floors including ground.
So, they have 7 options to leave the lift.
∴ total ways in which persons can leave the lift = 75
As the number of ways in which all persons leave in a different floor can be given by: 7× 6× 5× 4× 3 = 7P5
∴ P(that all leave lift in different floor) = 
Our answer matches with option (a)
∴ Option (a) is the only correct choice
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