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?	Select.
A) 14 1/7 days B) 11 1/7 days C) 16 1/7 days D) 17 1/7 days E) 24 1/7 days
17 1/7 days   17 1/7 days   1/30 + 1/40 = 7/120   120/7 = 17 1/7 days
<result>D</result>
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?