John completes a piece of work in 320 days, Rose completes the same work in 480 days. If both of them work together, then the number of days required to complete the work is?	Select:	A) 190	B) 192	C) 194	D) 196	E) 198

Rationale: "if a can complete a work in x days and b can complete the same work in y days , then , both of them together can complete the work in x y / x + y days . that is , the required no . of days = 320 × 480 / 800 = 192 days answer is b"
Answer: B