A, B and C can do a piece of work in 24 days, 30 days and 60 days respectively. They began the work together but C left 4 days before the completion of the work. In how many days was the work completed?	Choose the correct choice from the following options:
A) 10 days B) 11 days C) 13 days D) 21 days E) 31 days

Rationale: one day work of a , b and c = 1 / 24 + 1 / 30 + 1 / 60 = 11 / 120 work done by a and b together in the last 4 days = 4 * ( 1 / 24 + 1 / 30 ) = 3 / 10 remaining work = 7 / 10 the number of days required for this initial work = 7 days . the total number of days required = 4 + 7 = 11 days . answer : b
Answer: B