Solution:
Solution
A person can alight at any one of $$n$$ floors.Therefore, the number of ways in which $$m$$ passengers can alight at $$n$$ floors is $$n\times n\times n\times ...\times n(m$$-times$$)={ n }^{ m }.$$
The number of ways in which all passengers can alight at different floors is $$\displaystyle ^{ n }{ { C }_{ m } }\times m!={}^{ n }{ { P }_{ m } }.$$
Hence, required probability $$\displaystyle =\frac { ^{ n }{ { P }_{ m } } }{ { n }^{ m } } .$$
