On one hand, my book calls both electrons and holes intrinsic charge carriers of a semiconductor, and on the other, it states the relation x = y = n, where x, y and n stand for the number of electrons, holes and intrinsic charge carriers respectively. Shouldn't it be n = x+y instead?
Normally what we call the intrinsic charge carrier concentration, that I note $n_i$ is the number of charge of any kind (not their) sum. It is a convention to build the theory nothing more. Having defined something like $n'_i = e + h$ would have make the equations much more ugly.
This will be of use latter, because even though the semiconductor is not intrinsic the relation
$$e\cdot h = n_i^2$$
will be verified.
Notice that your case verify this.
It is a terrible idea to use the notation $e, h$ (especially e) as it will be confused with the charge.
If you are new to semiconductors I recommend you to read the two dedicated chapters of Ashcroft and Mermin. They are clear and give a good baseground.