Printing presses and newspapers

Lets look at it step by step.

6 PP print 5000 NP --> 4 hrs

3PP print 5000 NP --> 8 hrs ( Think of this. Now we have half the number of PP so it will double the time to do the same work)

3 PP print 1 NP ---> 8 / 5000 hrs

3 PP print 3000 NP ---? (8 / 5000) * 3000 = 4.8 hrs = 4 hrs + (.8)60 mins = 4 hrs 48 mins


Thus Answer should be C. Hope this helps.

6 press take 4 hrs to print 5000
3 press take 4 hrs to print 2500
3 press print 2500 copies in 4 hrs
3 press print 3000 copies in 4 * 3000/2500 = 4 4/5 hrs
= 4 hrs 48 minc
IMO C

2011mbaspirant wrote:If it takes 6 printing presses 4 hours to print 5000 newspapers, how long would it take 3 presses to print 3000 news papers?
a) 3 hrs, 20 mins
b) 4 hrs, 20 mins
c) 4 hrs, 48 mins
d) 5 hrs, 48 mins
e) 6 hrs, 50 mins

I am having trouble solving such problems. Please provide an explanation with your answer.
Thanks in advance.

First, you have to observe that papers printed are proportional to the number of printing presses and proportional to the time for which they work.

Hence, you can view the equation as papers = time * number

method 1 :

first case, we have number = 6, time = 4, and papers = 5000.
second case number = 3, time = x , and papers = 3000.

OR

(6 * 4) / ( 3 * x ) = ( 5000 /3000)

x= 4.8 hrs or 4 hours 48 mins. .


Method 2 :

see that number of machines is decreasing by 50% or has become .5 of its original value.

papers printed is decreasing by 40% ( 5000 -> 3000) or has become .6 of its original value.

to find the % increase in time, just substitute these values in our equation papers = time * number.

.6 = x * .5 or x = 1.2 i.e time is increasing by 20 % or 1/5th or original ( 1/5 of 4 * 60 mins = 48 mins)

the new time will be 4 + 48 mins or 4 hrs 48 mins.