Help with cardinalities

Let A = {a, b, c, d, e} and B = {0, 1}.


why is the cardinality of |A × A| = 25?

Not sure where the 25 came from

The cardinality of a set is the number of items in that set. The set A X A has 25 elements, which are the following:

(a,a)..(b,a)..(c,a)..(d,a)..(e,a)
(a,b)..(b,b)..(c,b)..(d,b)..(e,b)
(a,c)..(b,c)..(c,c)..(d,c)..(e,c)
(a,d)..(b,d)..(c,d)..(d,d)..(e,d)
(a,e)..(b,e)..(c,e)..(d,e)..(e,e).


Clearly, from the list, we can see that |A x A| = 25.