It takes one machine 7 hours to complete a production order and another machine 3 hours to complete the same order. How many hours would it take both amhcines working simultaneously at their respective rates to complete the order? Options:
A) a) 7/12  B) b) 1 1/2  C) c) 1 5/7  D) d) 3 1/2  E) e) 2 6/11
RT = W   Given:   R = 1/7 + 1/4 = 11/28   T = ?   W = 1   T = 1 / (11/28) = 28/11 = 2 6/11   Answer: e) 2 6/11
<result>E</result>
It takes one machine 7 hours to complete a production order and another machine 3 hours to complete the same order. How many hours would it take both amhcines working simultaneously at their respective rates to complete the order?