How much Z?

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colakumarfanta: Senior | Next Rank: 100 Posts; Posts: 49; Joined: Mon May 03, 2010 2:55 am; Thanked: 1 times

by colakumarfanta » Thu May 20, 2010 9:46 am

x is 40% less than y, z is 20% more than x, z is how much less than y?

Is it [spoiler]28%[/spoiler]

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Source: Beat The GMAT — Problem Solving | Thu May 20, 2010 9:46 am

kikor65: Newbie | Next Rank: 10 Posts; Posts: 3; Joined: Sat Mar 14, 2009 7:22 am

by kikor65 » Thu May 20, 2010 10:01 am

Plug in a value for Y (I like to use 100 whenever possible as it is easy to manipulate with %s)

If y = 100 then x = 60
Therefore, y = 72

(100 - 72)/100 * 100 = 28%

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debmalya_dutta: Master | Next Rank: 500 Posts; Posts: 385; Joined: Sun Jul 12, 2009 10:16 pmFollowed by: 2 members; Thanked: 29 times; GMAT Score:710

by debmalya_dutta » Thu May 20, 2010 11:15 am

x=0.6 y and z=1.2x
=> z= 1.2 (0.6y) = 0.72y
Hence z is (1-0.72)*100 or 28% less than y

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stephen@knewton: GMAT Instructor; Posts: 22; Joined: Mon Mar 15, 2010 2:42 pmFollowed by: 4 members; Location: Brooklyn, NY; Thanked: 14 times

by stephen@knewton » Thu May 20, 2010 1:11 pm

Great work from both responders, but let me offer a quick endorsement for the strategy proposed by kikor65! Whenever you are dealing with a percentage problem, plugging in 100 provides a quick and fool-proof way to handle the calculations. The algebraic method always WORKS, but the more complex the problem, the more time you'll save by plugging in. And time, ladies and gentlemen, is money! Or, points, which indirectly correlate to money

Cheers,

Stephen
GMAT Instructor
Knewton Inc.

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indiantiger: Master | Next Rank: 500 Posts; Posts: 362; Joined: Fri Oct 02, 2009 4:18 amFollowed by: 1 member; Thanked: 26 times

by indiantiger » Thu May 20, 2010 4:02 pm

x = y - 40/100*y = 60y/100
z = x + 20/100*x = 120x/100 --(1)
substitute value of x in (1)
120*60/100*100 = 12*6/100 = 18/25 = .72 or 72% of y
calculate the answer by doing
y - z/y = (y - 72/100*y)/y = .28

"Single Malt is better than Blended"

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frank1: Legendary Member; Posts: 537; Joined: Fri Jan 22, 2010 10:06 pmFollowed by: 1 member; Thanked: 14 times

by frank1 » Thu May 20, 2010 6:44 pm

kikor65 wrote:Plug in a value for Y (I like to use 100 whenever possible as it is easy to manipulate with %s)

If y = 100 then x = 60
Therefore, y = 72

(100 - 72)/100 * 100 = 28%

lol ...
yes i think this is the easist way ...
one should be careful about assuming the largest value 100 in this case Y.....(assming X=100 or z=100 adds up complications)

but in this reply,
u wrote y=72.....(i head rolled once...how much y=72 actaully z=72)...but later relaized that it was mistake....
any way minor but can sometime make a huge difference....during linear flow of mind...lol

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