DS Question

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giatch: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Thu Oct 09, 2008 10:35 am

by giatch » Wed Dec 31, 2008 9:13 pm

Is x> y?

1. 2x> y

2. y <0

Anyone have any idea of how you go about solving this? Like how would you pick numbers to get a solution? or is there some method to approach this question?

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Source: Beat The GMAT — Data Sufficiency | Wed Dec 31, 2008 9:13 pm

daisy: Junior | Next Rank: 30 Posts; Posts: 13; Joined: Wed Dec 31, 2008 2:20 pm; Location: London

by daisy » Thu Jan 01, 2009 4:33 am

IMO (C)

Statement 1: 2x > y

Lets say x = 1/2 and y = 3/4. Therefore, x < y
Lets say x = 1 and y = 1. Therefore x = y
Lets say x = 2 and y = 1. Therefore x > y

Above all three stated statements are contradicting each other.
Therefore, statement 1 -> Insufficient.

Statement 2: y < 0

No info about x. Hence statement 2 -> Insufficient.

Lets take both statement together.

x >= 0, y < 0. Therefore, x > y
x > -(1/3), y = -1, therefore x > y
x = -(1/2), y = -(1/2). => Not possible (It invalidates the 1st statement)
Try any other negative combination which satisfy both statements, X will always greater than Y.

Hence, both statements together are sufficient. Choose (C).

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maihuna: Legendary Member; Posts: 1578; Joined: Sun Dec 28, 2008 1:49 amFollowed by: 9 members; Thanked: 82 times; GMAT Score:720

by maihuna » Thu Jan 01, 2009 4:41 am

Itoo C why?
X > Y/2
Y is negative

so how it will turn out to be: IF Y = -4 X > -2 i.e. X = -1 that way x will be greater than y

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daisy: Junior | Next Rank: 30 Posts; Posts: 13; Joined: Wed Dec 31, 2008 2:20 pm; Location: London

by daisy » Thu Jan 01, 2009 4:46 am

maihuna wrote:Itoo C why?
so how it will turn out to be: IF Y = -4 X > -2 i.e. X = -1 that way x will be greater than y

That's what I said in my previous post,

Daisy wrote: Try any other negative combination which satisfy both statements, X will always greater than Y.

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logitech: Legendary Member; Posts: 2134; Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members; Thanked: 237 times; GMAT Score:730

Re: DS Question

by logitech » Thu Jan 01, 2009 12:10 pm

giatch wrote:Is x> y?

1. 2x> y

2. y <0

Anyone have any idea of how you go about solving this? Like how would you pick numbers to get a solution? or is there some method to approach this question?

We are trying to prove whether X-Y > 0

1. 2x> y

2x - y > 0

We can simplfy this to X-Y so insuf

2. y <0

No information about X - INSUF

TOGETHER

2x - y > 0

- y > 0 [ Note the sign change ]

Let's add these two equations:

2x - 2y > 0

OR

X - Y > 0 Tataaam!!!

Hence, C

LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"

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giatch: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Thu Oct 09, 2008 10:35 am

clarify

by giatch » Thu Jan 01, 2009 3:55 pm

1. 2x> y

2x - y > 0

We can simplfy this to X-Y so insuf
---------

How do you simply 2x-y to x-y? Or do you mean, you cannot simply, so insufficient?

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logitech: Legendary Member; Posts: 2134; Joined: Mon Oct 20, 2008 11:26 pmFollowed by: 25 members; Thanked: 237 times; GMAT Score:730

Re: clarify

by logitech » Thu Jan 01, 2009 4:22 pm

giatch wrote:1. 2x> y

2x - y > 0

We can simplfy this to X-Y so insuf
---------

How do you simply 2x-y to x-y? Or do you mean, you cannot simply, so insufficient?

BE CAREFUL!!

X=2 Y =3

2x - Y = 4-3 = 1 > 0

X-Y = 2-3 = -1 < 0

ONCE AGAIN!! BE CAREFUL!!

LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Thu Jan 01, 2009 4:29 pm

Giatch,

Here's one way:

Q: Is x>y (u can rephrase this as Is x-y>0 then prove it like some of the other solutions have shown but I will leave it as is to illustrate it by picking numbers

Note: x and y does not have to be integers since its not given

Since u had asked about picking numbers here is one way to solve by picking numbers

Stmt I

2x > y

Is x >y

x=1/2 y=9/10

2x > y but x > y NO

x=10 y=1

2x>y and x>y YES

2 different answers(YES/NO) INSUFF

Stmt II

y<0

No info about x

INSUFF

Together

2x>y (1)

y<0 or 0>y (2)

Add Inequalities facing same direction((1) and (2)):

2x+0>y+y

2x>2y

Divide by 2 on both sides(inequality does not change since we are dividing by a positive number 2)

x>y

SUFF

Choose C)

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giatch: Junior | Next Rank: 30 Posts; Posts: 20; Joined: Thu Oct 09, 2008 10:35 am

ahh

by giatch » Thu Jan 01, 2009 4:47 pm

thanks guys for the help..
i get it now..

i was having a hard time figuring out which numbers to use..
i suppose for questions like this, if it is not specified that the variables are integers, start by picking #'s like 1/2, etc.

out of curiosity, would you start the stem assuming that the equation is true and then work your way to see if it is? or start off as it being false and trying to see if the answers agree?

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cramya: Legendary Member; Posts: 2467; Joined: Thu Aug 28, 2008 6:14 pmFollowed by: 11 members; Thanked: 331 times

by cramya » Thu Jan 01, 2009 5:01 pm

out of curiosity, would you start the stem assuming that the equation is true and then work your way to see if it is? or start off as it being false and trying to see if the answers agree

Hope I understood your question.

The question stem is what we need to find based on the information given in the 2 statements. The real task is to check if the information given in each of the statements by itself or together (depending on how it goes ) are SUFFICIENT to find what we need to (i.e x>y in this problem)

Eg: We need to find if x>y possibly from the 2 statements given.

When we take each of the statements by itself first and then together if needed we have to prove that its either INSUFFICIENT OR SUFFICIENT to get a defnite answer for what asked in the question stem.

If its a find the value question (eg: what is the value of x) then we must be able to find one definite value for x.

If its a YES or NO question then we must get a DEFINITE YES OR A DEFNITE NO from the stmts etc...

Check this out on some basic info on how to approach DS questions. Its always good to elimnate choices and then work with remaining choices. This way u would be increasing the chaces of getting a question correct.

https://www.gmathacks.com/data-sufficien ... -test.html

Hope this helps! Let us know if u have more questions.

Regards,
Cramya

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ronniecoleman: Legendary Member; Posts: 546; Joined: Sun Nov 16, 2008 11:00 pm; Location: New Delhi , India; Thanked: 13 times

by ronniecoleman » Thu Jan 01, 2009 11:10 pm

IMO C

x> y?

1. 2x> y

2. y <0

1) Picking postive numbers;

x = 1
y = 1

2x > y
but x = y

OUT

2) y < 0

x can be any number... OUT

togther...

------------------- ( y) ----------------------( 2x) ------------------(x) -----------------0

choose any value if 2x > y ( negatvie number line)
so x > y always ...

Admission champion, Hauz khaz
011-27565856

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