A and B can do a work in 20days, B and C can do it in 30days; A,B and C together can finish it in 40days. A and C together will do it in?	Select: A) 25 days B) 30 days C) 20 days D) 15 days E) 10 days

Rationale: a + b + c 1 day work = 1 / 40 a + b 1 day work = 1 / 20 b + c 1 day work = 1 / 30 a + c 1 day work = 2 * 1 / 40 - 1 / 20 + 1 / 30 = 1 / 30 a and c together will do the work in 30 days . answer is b
Answer: B