Working independently, machines A, B, C and D can do a certain assignment, in 4, 6, 8 and10 hours, respectively. If two machines work together at their individual rates, what is the ratio of the time it takes machines A and B to do the assignment to the time it takes machines C and D to do the assignment ?   5/9   27/50   50/27   3/32   32/3   Hint Half-n-half Clue