Ravi can do a piece of work in 30 days while Prakash can do it in 40 days. In how many days will they finish it together?\nOptions:\n(A) 19 1/7 days\n(B) 16 1/7 days\n(C) 14 1/7 days\n(D) 17 1/7 days\n(E) 13 1/7 days
Please answer and provide answer explanation.
(D)
1/30 + 1/40 = 7/120\n120/7 = 17 1/7 days.

Thus, the answer is (D)