A is twice as fast as B. If B alone can do a piece of work in 30 days, in what time can A and B together complete the work?	Choose the most appropriate option:
A) 13	B) 10	C) 16	D) 50	E) 23

Rationale: "option b explanation : a can do the work in 30 / 2 i . e . , 15 days . a and b ' s one day ' s work = 1 / 15 + 1 / 30 = ( 2 + 1 ) / 30 = 1 / 10 so a and b together can do the work in 10 days ."
Answer: B