I pulled this off but I want to hear from folks on their approaches

In normal printing mode, 20 printers can print 100 pages in 3 minutes. In economy mode, printers work 20% faster than in normal mode. How many printers are required to print 180 pages in 3 minutes in economy mode?

(C) 2008 GMAT Club - m24#24

* 25
* 28
* 29
* 30
* 32



Source: GMAT Club Tests - hardest GMAT Questions

normal mod = 100/20*3 = 5/3 PAGES/printer/minute

economy mode printer rate = 5/3 *1.2 = 2 pages/printer/minute

priner rate for 3 minutes = 6 pages/printer = 180 pages /30 printers

30

D

Method:

1) First find out the time required to print 1 page in 3 Minutes (here 3 Minutes because answer ask for the same) with 1 printer and you will find one printer prints 6 pages in 3 minutes after their percentage increase in economical speed.

(100 / 20) * (120 / 100) = 6 pages.

2) Once you find this it is easy to find for 180 pages how many printer requires. (30).

2) Once you find 6

In economy mode printers print 20% faster. Hence 20 printers will print 120 pages in 3 mins. You want 1.5 times of 120 pages, hence you multiply 1.5 * 20 printers (and don't touch the time at all, as we want to find out the number of pages in 3 mins) = 30 printers.

Hence, ANS - 30 printers

Normal mode rate = 100/(3*20)
Economy mode rate = 1.20 * 100/(3*20)

Now, let x be the number of economy mode printers.
Adding rates of all printers = Combined rate of printers

x * 1.20 * 100/(3*20) = 180/3
=>x = 30

20 printer, 100 page, 3 minutes
1 printer, 5 page, 3 minutes
in economy it is 20% faster
so,
1 printer, 5+1 page , 3 minutes
30 printer, 180 page, 3 minutes.
D is the answer