x% of y

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RadiumBall: Master | Next Rank: 500 Posts; Posts: 132; Joined: Thu Dec 02, 2010 2:49 am; Thanked: 5 times

by RadiumBall » Mon Mar 28, 2011 10:40 pm

x% of y is increased by x%. What is the result in terms of x and y?
A) 100xy + x
B) xy + x/100
C) 100xy + x/100
D) 100xy + xy/100
E) xy(x + 100)/10000

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Source: Beat The GMAT — Problem Solving | Mon Mar 28, 2011 10:40 pm

srcc25anu: Master | Next Rank: 500 Posts; Posts: 423; Joined: Fri Jun 11, 2010 7:59 amFollowed by: 2 members; Location: Seattle, WA; Thanked: 86 times

by srcc25anu » Mon Mar 28, 2011 10:50 pm

its E

as x% of y = xy/100

when this is increased by x%, xy/100 * [1+x/100]

which is equal to xy(100+x) / 10000

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force5: Legendary Member; Posts: 582; Joined: Tue Mar 08, 2011 12:48 amFollowed by: 6 members; Thanked: 61 times; GMAT Score:740

by force5 » Tue Mar 29, 2011 1:04 am

yes Its E, easy one....

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RadiumBall: Master | Next Rank: 500 Posts; Posts: 132; Joined: Thu Dec 02, 2010 2:49 am; Thanked: 5 times

by RadiumBall » Tue Mar 29, 2011 11:30 pm

Thanks
Correct OA: E

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avdhutgmat: Newbie | Next Rank: 10 Posts; Posts: 4; Joined: Mon Mar 28, 2011 10:20 am

by avdhutgmat » Mon Apr 04, 2011 9:21 am

we can do it by putting values too
consider x=10 and y=100 .
if x% of y i.e. 10 is increased by 10% means by 1.
hence look for value which gives value as 11

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tpr-becky: GMAT Instructor; Posts: 509; Joined: Wed Apr 21, 2010 1:08 pmFollowed by: 85 members; Location: Irvine, CA; Thanked: 199 times; GMAT Score:750

by tpr-becky » Tue Apr 05, 2011 8:33 am

If you aren't perfect at algebra you can simply pick values most of the time when there are variables in the answer choices - I picked x=5 and y = 200

5% of 200 = 10.

increasing 10 by 5% gives you 10.5

Then plug your original x and y into the answers:

A) - way too big
B) 1000 + 5/100 - nope
c) Too big (100,000 +5)/100
D - nope
E) 1000(105)/10000 - reduces to 105/10 - which is 10.5 - correct answer.

Becky
Master GMAT Instructor
The Princeton Review
Irvine, CA

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