It takes 40 identical printing presses 9 hours to print 500,000 papers. How many hours would it take 30 of these printing presses to print 500,000 papers? Choose the correct choice from the following answers.
A) 9
B) 10
C) 11
D) 12
E) 13
40 printing presses can do 1/9 of the job each hour.   30 printing presses can do 3/4*1/9 = 1/12 of the job each hour.   The answer is 12.
<result>D</result>
It takes 40 identical printing presses 9 hours to print 500,000 papers. How many hours would it take 30 of these printing presses to print 500,000 papers?