A is twice as good a workman as B and they took 9 days together to do the work B alone can do it in? Select:
A) 25 days
B) 88 days
C) 21 days
D) 27 days
E) 13 days

Rationale: "wc = 2 : 1 2 x + x = 1 / 9 x = 1 / 27 = > 27 days answer : d"
Answer: D