P & C

The ordered pairs (x, y) satisfying the given condition are (1, 1), (2, 2),...,(19, 19); (1, 10), (2, 11), (3, 12),...,(9, 18); (10, 1), (11, 2),...,(18, 9). As the domain is A, we must assign values to each x=1, 2,..., 19. Now, for x=1, we have two choices for y(1 and 10), similarly for x=2, 3,...,18 whereas for x=19 we have only one possible value of y. Therefore the answer will be 2¹⁸.

Is (c) the correct answer?

Tell me how !!