A question from princeton review

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ferndinho: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Wed Jun 20, 2007 6:17 am

by ferndinho » Tue Jan 13, 2009 6:29 am

I am just beginning my GMAT prep (2nd time) and came across a problem in the princeton review cracking the GMAT book...it is on page 70...

The output of a factory was increased by 10% to keep up with rising demand. To handle the holiday rush, this new output was increased by 20%. By approximately what % would the output now have to be decreased in order to restore the original output?
a)20%
b)24%
c)30%
d)32%
e)70%

They list B 24% as the answer...I see no other answer than D32%. Am I completely missing something or is this a book mistake?

Thanks

Source: Beat The GMAT — Problem Solving | Tue Jan 13, 2009 6:29 am

Hovey25: Junior | Next Rank: 30 Posts; Posts: 16; Joined: Sun Dec 14, 2008 9:19 pm; Location: Wausau, WI; Thanked: 2 times

by Hovey25 » Tue Jan 13, 2009 7:50 am

You probably have a slight error in your calculation...

My guess is you took a number lets say 1000

10% increase 1000*1.1=1100 additional 20% increase 1100*1.2=1320

Here is your mistake 1320-1000=320...320/1000=32%

You need to take the decrease from the output after the 10 and 20% increases, not the original output

So...1320-1000=320...320/1320=24.24% round to 24%

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