A, Band C can do a piece of work in 11 days, 5 days and 55 days respectively, working alone. How soon can the work be done if A is assisted by Band C on alternate days? Choose one
A) 5 days
B) 8 days
C) 9 days
D) 10 days
E) 11 days

Rationale: ( a + b ) ' s 1 day ' s work = 1 / 11 + 1 / 5 = 16 / 55 ( a + c ) ' s 1 day ' s work = 1 / 11 + 1 / 55 = 6 / 55 work done in 2 day ' s = 16 / 55 + 6 / 55 = 2 / 5 2 / 5 th work done in 2 days work done = 5 / 2 * 2 = 5 days answer : a
Answer: A