A and B can finish a work in 10 days while A alone can do the same work in 20 days. In how many days B alone will complete the work? Choose the correct choice.
A) 20 days B) 48 days C) 98 days D) 31 days E) 22 days

Rationale: "b = 1 / 10 – 1 / 20 = 1 / 20 = > 20 days answer : a"
Answer: A