Working alone, machine X can manufacture 1,200 nails in 12 hours. Working together, machines X and Y can manufacture 1,200 nails in 5 hours. How many hours does it take machine Y to manufacture 1,000 nails working alone?  Choose the correct option
A) 3 9/17
B) 5 1/3
C) 7
D) 7 1/7
E) 8 4/7
rate of machine x = 1200/12   (1200/12 + y)5=1200   y=700/5   700/5 * t = 1000   t=7 1/7   7 1/7.
<result>D</result>
Working alone, machine X can manufacture 1,200 nails in 12 hours. Working together, machines X and Y can manufacture 1,200 nails in 5 hours. How many hours does it take machine Y to manufacture 1,000 nails working alone?