There is a total of 84 marbles in a box, each of which is red, green, blue, or white. If one marble is drawn from the box at random, the probability that it will be white is 1/4 and the probability that it will be green is 2/7. What is the probability that the marble will be either red or blue?
Choose one
A) 3 / 7 B) 11 / 14 C) 13 / 28 D) 19 / 28 E) 29 / 42

Rationale: p ( red or blue ) = 1 - p ( white ) - p ( green ) = 28 / 28 - 7 / 28 - 8 / 28 = 13 / 28 the answer is c .
Answer: C