A bag consists of 20 marbles, of which 5 are blue, 7 are red, and the remainder are white. If Lisa is to select a marble from the bag at random, what is the probability that the marble will be red or white?
Choose the most appropriate option.
A) 3 / 4
B) 2 / 4
C) 1 / 4
D) 1 / 8
E) 1 / 16

Rationale: "bag consists of 20 marbles , of which 5 are blue , 7 are red remainder are white . so , white = 20 - 5 - 7 = 8 . probability that the marble will be red or white = probability that the marble will be red + probability that the marble will be white probability that the marble will be red or white = 7 / 20 + 8 / 20 = 15 / 20 = 3 / 4 hence , answer will be a ."
Answer: A