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?  Choose one:
A) 17 1/7 days  B) 5 days  C) 6 days  D) 9 days  E) 10 days
Explanation:   1/30 + 1/40 = 7/120   120/7 = 17 1/7 days   17 1/7 daysnswer: 17 1/7 days
<result>A</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?