Machines X and Y produce bottles at their respective constant rates. Machine X produces k bottles in 4 hours and machine Y produces k bottles in 5 hours. How many hours does it take machines X and Y , working simultaneously , to produce 10k bottles? Options:
A) 8 2/3  B) 12 5/3  C) 15  D) 18  E) 22 2/9
x rate = k/4   y rate = k/5   k/4 + k/5 = 10k / T   solving T = 200/9 = 22 (2/9)   Answer 22 2/9
<result>E</result>
Machines X and Y produce bottles at their respective constant rates. Machine X produces k bottles in 4 hours and machine Y produces k bottles in 5 hours. How many hours does it take machines X and Y , working simultaneously , to produce 10k bottles?