If it would take one machine 15 minutes to fill a large production order and another machine 20 minutes to fill the same order, how many minutes would it take both machines working together, at their respective rates, to fill the order?
Choose the correct choice from the following answers: A) 4 1/60 B) 5 C) 5 5/11 D) 5 1/2 E) 8 4/11
Since , Machine 1-M1 take 15 mins to fill the order   The work done by M1 in a min = 1/15   Machine 2- M2 take 20 mins to fill the same order   and work done by M2 in a min = 1/20   Total work done by M1 and M2 in a min = 1/15 + 1/20 = 7/60   Time needed for M1 and M2 to complete the order = 60/7 = 8 4/11   Answer 8 4/11
<result>E</result>
If it would take one machine 15 minutes to fill a large production order and another machine 20 minutes to fill the same order, how many minutes would it take both machines working together, at their respective rates, to fill the order?