A number of elements are:
(99-3) : 2 + 1 = 49 ( elements)
So in A 49 elements.
We have the recipe to calculate the elements in a set is:
(the final-the firstly):the distance of two adjacent numbers+1
lean to the recipe we have:
(99-3) : 2 + 1=49 (elements)
so A has 49 Elements