It takes 40 identical printing presses 15 hours to print 500,000 papers. How many hours would it take 30 of these printing presses to print 500,000 papers?  Options:	A) 16	B) 18	C) 20	D) 21	E) 24
40 printing presses can do 1/15 of the job each hour.   30 printing presses can do 3/4*1/15 = 1/20 of the job each hour.   The answer is 20.
<result>C</result>
It takes 40 identical printing presses 15 hours to print 500,000 papers. How many hours would it take 30 of these printing presses to print 500,000 papers?