A set of 10 new questions in each round Question: ( 1 of 10 ) David can finish a work in 9 days. William can finish the same work in 10 days while Richard can finish the work in 11 days. How long will it take to finish it if they work together? (A) 6 93/299 days or 6.311 days (B) 10 days (C) 3 93/299 days or 3.311 days (D) 7.5 days