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rabab: Master | Next Rank: 500 Posts; Posts: 132; Joined: Fri Sep 05, 2008 10:19 pm; Location: Bangladesh; Thanked: 1 times

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by rabab » Thu Oct 09, 2008 9:08 am

The output of a factory was raised by 10% to keep up with rising demand. To handle the holiday rush, this new output was increased by 20%. By approximately what percent would the output now have to be decreased in order to restore the original output?

a. 20%
b. 24%
c. 30%
d. 32%
e. 79%

IOM 32%.

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Source: Beat The GMAT — Problem Solving | Thu Oct 09, 2008 9:08 am

toudavis: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Fri Jun 20, 2008 7:36 am

by toudavis » Thu Oct 09, 2008 9:13 am

Agreed.

Start with 100(1.10) = 110
110(1.20) = 132

(Orig - New)/New = (100-132)/100 = 32/100 or 32%

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rabab: Master | Next Rank: 500 Posts; Posts: 132; Joined: Fri Sep 05, 2008 10:19 pm; Location: Bangladesh; Thanked: 1 times

by rabab » Thu Oct 09, 2008 9:19 am

But PR says the answer should be 24%. I don't get it.

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mental: Master | Next Rank: 500 Posts; Posts: 145; Joined: Mon Sep 29, 2008 1:14 am; Thanked: 13 times

by mental » Thu Oct 09, 2008 9:26 am

IMO B

rabab and toudavis

going with ur values
Start with 100(1.10) = 110
110(1.20) = 132

current level is 132, old level 100

to bring 132 to 100 we have to reduce by 32

so 32 is how much percent of 132:
32/132 is approx 24%

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rabab: Master | Next Rank: 500 Posts; Posts: 132; Joined: Fri Sep 05, 2008 10:19 pm; Location: Bangladesh; Thanked: 1 times

by rabab » Thu Oct 09, 2008 9:32 am

mental wrote:IMO B

rabab and toudavis

going with ur values
Start with 100(1.10) = 110
110(1.20) = 132

current level is 132, old level 100

to bring 132 to 100 we have to reduce by 32

so 32 is how much percent of 132:
32/132 is approx 24%

I see. Thanks for the help!

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VP_Jim: GMAT Instructor; Posts: 1223; Joined: Thu May 01, 2008 3:29 pm; Location: Los Angeles, CA; Thanked: 185 times; Followed by:15 members

by VP_Jim » Thu Oct 09, 2008 4:31 pm

Nothing to add here really - the explanation above (from mental) is fine. Start with 100 and then figure it out from there.

I did want to say, though, that this is a classic GMAT trap: tricking people into saying that the percent decrease from x to y would be the same as the percent increase from y to x (in this case, the percent decrease from 132 to 100 is not the same as the percent incresae from 100 to 132).

Be careful!

Jim S. | GMAT Instructor | Veritas Prep