Ravi can do a piece of work in 24 days while Prakash can do it in 40 days. In how many days will they finish it together? Choose the correct option
A) 15
B) 16
C) 17
D) 18
E) 10

Rationale: "1 / 24 + 1 / 40 = 1 / 15 15 days answer : a"
Answer: A