David completes a piece of work in 5 days, John completes the same work in 9 days. If both of them work together, then the number of days required to complete the work is?
Options:  A) 3.2 days  B) 8 days  C) 10 days  D) 12 days  E) 14 days
IfA can complete a work in x days and B can complete the same work in y days, then, both   of them together can complete the work in x y/ x+ y days.   That is, the required No. of days = 5 × 9/14= 3.2 days   3.2 daysnswer : 3.2 days
<result>A</result>
David completes a piece of work in 5 days, John completes the same work in 9 days. If both of them work together, then the number of days required to complete the work is?