1/30 + 1/40 = 7/120
120/7 = 17 1/7 days
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?
[A] 17 1/7
[B] 17 1/5
[C] 17 1/8
[D] 17 1/1
[E] 17 1/2