A set of 10 new questions in each round Question: ( 2 of 10 ) David can finish a work in 13 days. Richard can finish the same work in 18 days while Joseph can finish the work in 23 days. How long will it take to finish it if they work together? (A) 13.5 days (B) 5 647/947 days or 5.683 days (C) 18 days (D) 10 647/947 days or 10.683 days