1/15 + 1/30 = 3/30
10/1 = 10 days
Ravi can do a piece of work in 15 days while Prakash can do it in 30 days. In how many days will they finish it together?
[a] 11 days
[b] 9 days
[c] 8 days
[d] 12 days
[e] 10 days