A can finish a piece of work in 5 days. B can do it in 10 days. They work together for two days and then A goes away. In how many days will B finish the work?
Choose the correct answer:
A) 4 days  B) 6 days  C) 7 days  D) 1 days  E) 3 days

Rationale: "a 4 days 2 / 5 + ( 2 + x ) / 10 = 1 = > x = 4 days"
Answer: A