Mangala completes a piece of work in 9 days, Raju completes the same work in 21 days. If both of them work together, then the number of days required to complete the work is
Pick one.
A) 6 days
B) 7 days
C) 8 days
D) 9 days
E) 11 days
If A 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 = 9 Ã— 21/30 = 6 days.   6 days
<result>A</result>
Mangala completes a piece of work in 9 days, Raju completes the same work in 21 days. If both of them work together, then the number of days required to complete the work is