This is the translated version of the question:
Allocating randomly 40 balls in 50 bins, what is the probability that a certain cell contains exactly 30 balls? What is the probability that a certain bin contains k balls, for k being 0,1,2,3,...,40?
I really don't know how to start this problem. Maybe a single hint is all I need to do this problem. It is given in my exercise book, and I don't have any solution for this.
The question implies that we are choosing one cell (or bin) and examining whether that cell gets $30$ balls or not.
In that case we have a fixed probability per ball of $\frac{1}{50}$ for getting the ball and $\frac{49}{50}$ for not getting it in that cell. We also have $\binom {40}{30}$ different sequences for getting that set of outcomes, giving the probability
$$\binom {40}{30}\frac{1^{30}49^{10}}{50^{40}}$$
for a given cell of getting $30$ balls exactly.
The case for $k$ balls in a given cell follows straightforwardly.