**Solution:** By the definition of the cartesian product,

P × Q = {(a, r ), (b, r), (c, r)} and Q × P = {(r, a), (r, b ), (r, c)}

Since, by the definition of equality of ordered pairs, the pair (a, r) is not equal to the pair

(r, a), we conclude that P × Q ¹ Q × P.

However, the number of elements in each set will be the same.