If it takes 6 identical printing presses 4 hours to print 5000 newspapers, how long would it take to print 3 of these presses to print 3000 newspapers?
A. 3 hours, 20 minutes
B. 4 hours, 20 minutes
C. 4 hours, 48 minutes
D. 5 hours, 48 minutes
E. 6 hours, 50 minutes
source: www.800score.com
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The key information is the printing throughput per press (T), as they are said to be identical.
Let T be the throughput per press, N the number of newspapers printed, H the numebr of hours and P the numer of presses used:
T = N / (H*P)
No for N=5000, H=4 and P=6 we get T = 5000/24.
The time we now seek is obtained by calculating H'=N'/(P'xT) = 3000/[3*(5000/24)]=24*1000/5000=
=24*2000/10000=48000/10000=4.8 hours, almost five hours then.
Looking at the options list we have option B. and option C. with more than 4 and less than five hours. However those 20 minutes in option B. are less than half an hour (30 minutes). This means that the amount of hours whould be less than 4.5 but we ended with 4.8 hours and the decimal part of this value (0.8) multiplied my 60 minutes, actually leads to 48 minutes, as we find in option C. So we take C.
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