Let n(S)= 10C2 =
10
×
9
2
×
1
= 45
(a) Let A: Product of the members is 0
= {(0. 1) (0, 2) (0, 3) (0, 4) (0, 5) (0, 6) (0, 7) (0, 8) (0, 9)}
n(A) = 9
(b) Let B: sum is less than 4
B = {(0, 1) (0, 2) (0, 3) (1, 2)} n(B) = 4
(c) Let C: one number is 3 times the other
C = ((1,3) (2,6)(3,9)} ⇒ n(C) = 3