Machines A and B produce bottles at their respective constant rates. Machine A produces k bottles in 2 hours and machine B produces k bottles in 5 hours. How many hours does it take machines A and B, working simultaneously, to produce 14k bottles? Pick one
A) 14
B) 16
C) 18
D) 20
E) 22
A's rate = k/2   B's rate = k/5   k/2 + k/5 = 7k/10   14k / (7k/10) = 20 hours   The answer is 20.14  / (7 /10)= 
<gadget id="calculator">14  / (7 /10)</gadget>
<output>20</output>
20 hours   The answer is 20.
<result>D</result>
Machines A and B produce bottles at their respective constant rates. Machine A produces k bottles in 2 hours and machine B produces k bottles in 5 hours. How many hours does it take machines A and B, working simultaneously, to produce 14k bottles?