The marginal distribution for gender tells you the probability that a randomly selected person taken from this sample is either male or female, regardless of their blood type.
In this case, we have total sample size of 714 people. Of these, 379 are male and 335 are female. Then the marginal probability mass function would be
where G is a random variable taking on one of two values (male or female).
Given a function <em>g(x)</em>, its derivative, if it exists, is equal to the limit
The limit is some expression that is itself a function of <em>x</em>. Then the derivative of <em>g(x)</em> at <em>x</em> = 1 is obtained by just plugging <em>x</em> = 1. In other words, find <em>g'(x)</em> - and this can be done with or without taking a limit - then evaluate <em>g'</em> (1).
Alternatively, you can directly find the derivative at a point by computing the limit
But this is essentially the same as the first method, we're just replacing <em>x</em> with 1.
Yet another way is to compute the limit
but this is really the same limit with <em>h</em> = <em>x</em> - 1.
You do not compute <em>g</em> (1) first, because as you say, that's just a constant, so its derivative is zero. But you're not concerned with the derivative of some <em>number</em>, you care about the derivative of a function that depends on a <em>variable.</em>