Newspaper

jain2016 wrote:If it takes 6 identical printing presses exactly 4 hours to print 5000 newspaper, how long would it take 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

Use the following formula:
(workers)(time)/output = (workers)(time)/output

Since 6 presses require 4 hours to yield an output of 5000 newspapers, and we must determine the number of hours required for 3 presses to yield an output of 3000 newspapers, we get:

(6*4)/5000 = (3x)/3000
24/5 = 3x/3
24/5 = x
x = 24/5 = 4 + 4/5 hours = 4 hours, 48 minutes.

The correct answer is C.

Hi GMATGuruNY & Rich ,

Thank you so much for your reply, but can you please do let me know whats wrong with my method?

Many thanks in advance.

SJ

jain2016 wrote:So 3000 newspaper with 1 press in 1 hour = 3000/625/3, it becomes 3000*3/625

Here, you correctly determine that the time for 1 press to produce 3000 newspapers = (3000*3)/625 hours.

Now 3000 newspaper with 3 presses will be = 3000*3*3/625 right?

This line of reasoning is incorrect.
Rate and time are RECIPROCALS.
Since 3 presses work at 3 TIMES THE RATE of 1 press, the time for 3 presses will be 1/3 THE TIME for 1 press.
Since the time for 1 press = (3000*3)/625 hours, the time for 3 presses = (1/3) * (3000*3)/625 = 3000/25 = 600/125 = 120/25 = 4 + 4/5 hours = 4 hours, 48 minutes.

The following approach might be easier:

Since in 1 hour each press produces 625/3 newspapers, the number of newspapers produced by 3 presses in 1 hour = (3)(625/3) = 625.
Since the rate for 3 presses = 625 newspapers per hour, the time for 3 presses to produce 3000 newspapers = w/r = 3000/625 = 600/125 = 120/25 = 4 + 4/5 hours = 4 hours, 48 minutes.

jain2016 wrote:If it takes 6 identical printing presses exactly 4 hours to print 5000 newspaper, how long would it take 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

OAC

SJ

You could also think about it like this: if it takes 6 presses 4 hours to do 5000 papers, it should take 3 presses 8 hours to do 5000 papers. (Half as many presses should take twice as much time.) If it takes 3 presses 8 hours to do 5000 papers, it should take them 8 *(.6) hours to do 3000 papers. (3000 is 60% or .6 of 5000.) 8 * .6 = 4.8 hours. Answer is C