Question 77
The escalator of “Champion Butcher” metro station has this property that if $m$ persons are on it, its speed is $m^{-\alpha}$ where $\alpha$ is a positive constant number. Suppose that $n$ persons want to go upstairs by the escalator. If the length of the escalator is $l$, what is the least time required for these persons to go to upstairs? (Suppose the persons can use the escalator simultaneously at any time).
