In the binomial function, negative binomial function, poisson
distribution, I dont know what to do when we need to find a
variable X. For example, If X is exactly at 0, 1 , 2, etc. Then I
know that we only need to apply the formula and calculate it.
However, in some cases like X <= 2, X >= 5, X > 4, etc,
then I do not know how to calculate that X and how to apply the
formula....