Give a quick stream of consciousness before answering the following question. 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?
Options:
(A) 17 1/7
(B) 17 1/5
(C) 17 1/8
(D) 17 1/1
(E) 17 1/2
1/30 + 1/40 = 7/120
120/7 = 17 1/7 days
The answer: (A).