In 2 bags, there are to be put together 5 red and 12 white balls, neither bag being empty. How must the balls be divided so as to give a person who draws 1 ball from either bag-  Pick one.
A) 9 / 18 B) 9 / 16 C) 9 / 11 D) 9 / 12 E) 9 / 13

Rationale: ( 1 ) put 1 white in first bag , and all the remaining ball in second bag . probability = 12 × 0 + 12 × 51612 × 0 + 12 × 516 = 532532 ( 2 ) to maximize , we put 1 red in the first bag , and all the remaining in the second . probability = 12 × 1 + 12 × 43212 × 1 + 12 × 432 = 9 / 16 answer : b
Answer: B