A,B,C can do a piece of work in 11days, 20days and 55days respectively, working alone. How soon can the work be done if A is assisted by B and C on alternate days?
Pick one:
A) 2 B) 4 C) 8 D) 10 E) 12

Rationale: a + b 1 day work = 1 / 11 + 1 / 20 = 31 / 220 a + c 1 day work = 1 / 11 + 1 / 55 = 6 / 55 work done in 2 days = 31 / 220 + 6 / 55 = 55 / 220 = 1 / 4 1 / 4 work is done by a in 2 days whole work will be done in 2 * 4 = 8 days answer is c
Answer: C