R = {2, 3, 4, 5}
B = {4, 5, 6, 7, 8}
Two integers will be randomly selected from the sets above, one integer from set R and one integer from set B. What is the probability that the sum of the two integers will equal 9 ?	Choose the correct choice from the following answers:
A) 0.15 B) 0.20 C) 0.25 D) 0.30 E) 0.33

Rationale: the total number of pairs r , b possible is 4 * 5 = 20 . out of these 20 pairs only 4 sum up to 9 : ( 2 , 7 ) ; ( 3 , 6 ) , ( 4 , 5 ) and ( 5 , 4 ) . the probability thus is 4 / 20 = 0.2 . answer : b .
Answer: B