A is four times as fast as B. If B alone can do a piece of work in 60 days, in what time can A and B together complete the work?  Select the correct option.
A) 10  B) 12  C) 22  D) 28  E) 20

Rationale: a can do the work in 60 / 4 i . e . , 15 days . a and b ' s one day ' s work = 1 / 15 + 1 / 60 = ( 4 + 1 ) / 60 = 1 / 12 so a and b together can do the work in 12 days . answer : b
Answer: B