If x and y are positive, is 3x > 7y?

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mitzwillrockgmat: Master | Next Rank: 500 Posts; Posts: 124; Joined: Wed May 19, 2010 10:20 pm; Thanked: 3 times; GMAT Score:1100

If x and y are positive, is 3x > 7y?

by mitzwillrockgmat » Sat Jun 12, 2010 11:55 am

If x and y are positive, is 3x > 7y?

(1) x > y + 4

(2) -5x < -14y

I've seen alot of posts regarding this question but all are very confusing as some say answer is B while others D.

The answer provided is D though.

When i did this question in a practice test, i picked B but now knowing the answer, I tried working backwards.

Can anyone shed light on what the correct answer actually is & how to approach this question?

This is what I did:

1) I don't get it !

2) -5x<-14y

so x > -14y/-5

x > 2.8y

so 3x > 8.4y hence, 3x >7y

so stat sufficient

Quote

Source: Beat The GMAT — Data Sufficiency | Sat Jun 12, 2010 11:55 am

outreach: Legendary Member; Posts: 748; Joined: Sun Jan 31, 2010 7:54 am; Thanked: 46 times; Followed by:3 members

by outreach » Sat Jun 12, 2010 1:57 pm

Q is x>2.3y?

option 1

if y=1 then X>5
this satisfies Q
if y=-1 then x>4
this satisfies Q

hence A can be correct

option 2 u have already proved

hence D

mitzwillrockgmat wrote:If x and y are positive, is 3x > 7y?

(1) x > y + 4

(2) -5x < -14y

I've seen alot of posts regarding this question but all are very confusing as some say answer is B while others D.

The answer provided is D though.

When i did this question in a practice test, i picked B but now knowing the answer, I tried working backwards.

Can anyone shed light on what the correct answer actually is & how to approach this question?

This is what I did:

1) I don't get it !

2) -5x<-14y

so x > -14y/-5

x > 2.8y

so 3x > 8.4y hence, 3x >7y

so stat sufficient

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mitzwillrockgmat: Master | Next Rank: 500 Posts; Posts: 124; Joined: Wed May 19, 2010 10:20 pm; Thanked: 3 times; GMAT Score:1100

by mitzwillrockgmat » Sat Jun 12, 2010 2:54 pm

outreach wrote:Q is x>2.3y?

option 1

if y=1 then X>5
this satisfies Q
if y=-1 then x>4 *****value of x & y is positive

this satisfies Q

hence A can be correct

option 2 u have already proved

hence D

mitzwillrockgmat wrote:If x and y are positive, is 3x > 7y?

(1) x > y + 4

(2) -5x < -14y

I've seen alot of posts regarding this question but all are very confusing as some say answer is B while others D.

The answer provided is D though.

When i did this question in a practice test, i picked B but now knowing the answer, I tried working backwards.

Can anyone shed light on what the correct answer actually is & how to approach this question?

This is what I did:

1) I don't get it !

2) -5x<-14y

so x > -14y/-5

x > 2.8y

so 3x > 8.4y hence, 3x >7y

so stat sufficient

Hi, the question mentions that the value of x & y is positive so your second set of values are not correct. can show me some other values maybe which prove that the stat is sufficient?

Also, shed some light on why you decided to pick those plug in values?

Quote

Stuart@KaplanGMAT: GMAT Instructor; Posts: 3225; Joined: Tue Jan 08, 2008 2:40 pm; Location: Toronto; Thanked: 1710 times; Followed by:614 members; GMAT Score:800

by Stuart@KaplanGMAT » Sat Jun 12, 2010 7:37 pm

mitzwillrockgmat wrote:If x and y are positive, is 3x > 7y?

(1) x > y + 4

(2) -5x < -14y

We know that x and y are positive, so we can rephrase the question as:

is x/y > 7/3?

(1) x > y + 4

let's start by picking very small values: y=1 and x=6 (we could pick smaller values if we wanted, since we don't have to pick integers):

Is 6/1 > 7/3? YES

now let's try really big values:

y = 95, x=100

is 100/95 > 7/3? NO

accordingly, (1) is not sufficient alone.

Stuart Kovinsky | Kaplan GMAT Faculty | Toronto

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Quote

mitzwillrockgmat: Master | Next Rank: 500 Posts; Posts: 124; Joined: Wed May 19, 2010 10:20 pm; Thanked: 3 times; GMAT Score:1100

by mitzwillrockgmat » Sun Jun 13, 2010 5:06 am

Stuart Kovinsky wrote:
mitzwillrockgmat wrote:If x and y are positive, is 3x > 7y?

(1) x > y + 4

(2) -5x < -14y

We know that x and y are positive, so we can rephrase the question as:

is x/y > 7/3?

(1) x > y + 4

let's start by picking very small values: y=1 and x=6 (we could pick smaller values if we wanted, since we don't have to pick integers):

Is 6/1 > 7/3? YES

now let's try really big values:

y = 95, x=100

is 100/95 > 7/3? NO

accordingly, (1) is not sufficient alone.