A and B can together finish a work in 10days. They worked together for 5days and then B left. After another 5days, A finished the remaining work. In how many days A alone can finish the job?	Pick one: A) 10 B) 15 C) 20 D) 5 E) 30

Rationale: "a + b 5 days work = 5 * 1 / 10 = 1 / 2 remaining work = 1 - 1 / 2 = 1 / 2 1 / 2 work is done by a in 5 days whole work will be done by a in 5 * 2 = 10 days answer is a"
Answer: A