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Math Expert V
Joined: 02 Sep 2009
Posts: 58136
If x and y are both positive, is x greater than 4?  [#permalink]

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Difficulty:   85% (hard)

Question Stats: 48% (01:57) correct 52% (01:46) wrong based on 232 sessions

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If x and y are both positive, is x greater than 4?

(1) x > y
(2) In the coordinate plane, the point (x, y) lies outside a circle of radius 5 centered at the origin.

Kudos for a correct solution.

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Math Expert V
Joined: 02 Sep 2009
Posts: 58136
Re: If x and y are both positive, is x greater than 4?  [#permalink]

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Bunuel wrote:
If x and y are both positive, is x greater than 4?

(1) x > y
(2) In the coordinate plane, the point (x, y) lies outside a circle of radius 5 centered at the origin.

Kudos for a correct solution.

MANHATTAN GMAT OFFICIAL SOLUTION:

We are told that both x and y are positive, and we are asked whether x is greater than 4. There’s not much rephrasing we can do to this question, so let’s move on to the statements.

Statement (1): INSUFFICIENT. All we know here is that x is larger than y. It is still possible for x to be any positive number (y just has to be a smaller positive number).

Statement (2): INSUFFICIENT. If the point (x, y) lies outside a circle of radius 5 centered at the origin, then that point lies at a distance of more than 5 units away from (0, 0). In the coordinate plane, distance can be computed with the Pythagorean Theorem. We can rephrase this statement to say that x^2 + y^2 > 25. However, x can still be as small or as large a positive number as we wish.

Statement (1) and (2) together: INSUFFICIENT. We can definitely pick a very large value for x to satisfy the statements and answer the question with a “Yes.” Just make y smaller to make the first statement true, and if x is bigger than 5, then we’ll definitely have statement (2) true as well.

The trick is that we can pick a value of x that is not greater than 4 and still satisfy all the conditions. Let’s try picking x equal to 4 (this would give us an answer of “No” to the question). So we need to see whether there are any values of y that satisfy the following 3 conditions:

1. y is positive (from the stem).
2. y is less than 4 (that is, less than x).
3. x^2 + y^2 > 25.

Let’s plug 4 in for x in the last inequality. We get

16 + y^2 > 25

y^2 > 9

y > 3

(since y must be positive, we don’t have to worry about the negative possibilities)

The conditions become these: y is greater than 3 and less than 4. Any number between 3 and 4 satisfies the conditions. Notice that y is not restricted to integer values; nothing in the problem indicates that it should be. Thus, we still cannot definitively answer the question of whether x is greater than 4. There are other values of x less than 4 that will work; one tricky part of this problem is that those values of x are greater than 3.

The correct answer is E.
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Intern  Joined: 24 Feb 2015
Posts: 45
Re: If x and y are both positive, is x greater than 4?  [#permalink]

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1
2
St 1 => no info about the value of y => Insufficient

St 2 => (x, y) must satisfy the inequality : x^2 + y^2 > 25
Both points (1,6) & (6, 1) will satisfy this inequality
i.e. x can be greater than or even less than 4 => hence, insufficient

Combining both statements => (x, y) such that x > y & x^2 + y^2 > 25
We need to test only with points from Quadrant I since both x & y are positive
Both points (6,1) & (3.9, 3.5) will satisfy both the given conditions
We still do not get a definite YES/NO answer.

So, correct answer is E .......(Most Probably)
Manager  Joined: 02 Jul 2015
Posts: 102
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GMAT 1: 680 Q49 V33 Re: If x and y are both positive, is x greater than 4?  [#permalink]

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Answer as per me is C. only first quadrant is to be considered. As x>y, area between x=0 and x=y is to be considered. thus, C.

Bunuel, is the approach right?
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Re: If x and y are both positive, is x greater than 4?  [#permalink]

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2
Bunuel wrote:
If x and y are both positive, is x greater than 4?

(1) x > y
(2) In the coordinate plane, the point (x, y) lies outside a circle of radius 5 centered at the origin.

Kudos for a correct solution.

Given: x and y are both POSITIVE

Question : Is x>4?

Statement 1: x>y

Case 1: y = 1, x=3 i.e. x < 4
Case 2: y = 1, x=5 i.e. x > 4
NOT SUFFICIENT

Statement 2: In the coordinate plane, the point (x, y) lies outside a circle of radius 5 centered at the origin
i.e. $$x^2 + y^2 > 5^2$$
i.e. $$x^2 + y^2 > 25$$
Case 1: y = 4, x=3.5 i.e. x < 4
Case 2: y = 4, x=4.5 i.e. x > 4
NOT SUFFICIENT

Combining the two statements:
$$x^2 + y^2 > 25$$ and $$x>y$$
Case 1: $$y = 5/\sqrt{2} = 3.54$$, $$x=3.6$$ i.e. x < 4
Case 2: y = 4, x=4.5 i.e. x > 4

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Intern  Joined: 16 Mar 2015
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Re: If x and y are both positive, is x greater than 4?  [#permalink]

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Hi Experts,

I thought a lot on this but couldnt picture a values of x and Y when x>y -- Condition on combining both options.

Let us forget a equation x^2+Y^2 > 25 for a moment. Can you help me plotting the points on the graph which satisfies below conditions-

X Can be less then 4
X < Y
X,Y lie outside the circle of radius 5
Intern  B
Joined: 29 Aug 2017
Posts: 35
If x and y are both positive, is x greater than 4?  [#permalink]

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2
Bunuel wrote:
If x and y are both positive, is x greater than 4?

(1) x > y
(2) In the coordinate plane, the point (x, y) lies outside a circle of radius 5 centered at the origin.

Kudos for a correct solution.

Given: x > 0, y > 0
x > 4?

Statement 1:
x > y
This statement is insufficient to prove whether x > 4 because there are innumerable pairs of positive numbers where x > y and x < 4 such as (2, 1) and also x > y and x > 4 such as (5, 3), etc.

Statement 2:
Given: the point (x, y) lies outside a circle of radius 5 centered at the origin.
The point (x, y) lies on a circle of radius $$\sqrt{x^2 + y^2}$$ centered at the origin.
Since the point (x, y) lies outside the circle of radius 5, this implies that the radius of the circle with the point (x, y) is greater than 5.
So, $$\sqrt{x^2 + y^2} > 5$$
$$x^2 + y ^2 > 25$$
But, there are many pairs of numbers which satisfy this inequality without giving a definite answer on whether x > 4 such as (2, 5), (4, 4), (5, 1), etc.

Since the individual statements are insufficient individually, on combining them:
x > y and $$x^2 + y ^2 > 25$$
Since, x > y and x and y are positive
$$x^2 > y^2$$
$$x^2 + x^2 > y^2 + x^2 > 25$$
$$2x^2 > 25$$
x > $$5/\sqrt{2}$$
x > 3.5

But, combining the statements hasn't concluded if x > 4.
Hence, the statements are sufficient neither individually nor combined.

Therefore, the answer is E.
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If x and y are both positive, is x greater than 4?  [#permalink]

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This is how I solved. Hope it helps.

Posted from my mobile device
Attachments IMG_20190915_130727.jpg [ 2.97 MiB | Viewed 20 times ]

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Originally posted by EncounterGMAT on 23 Oct 2018, 09:37.
Last edited by EncounterGMAT on 15 Sep 2019, 00:47, edited 1 time in total.
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Re: If x and y are both positive, is x greater than 4?  [#permalink]

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1
Bunuel wrote:
If x and y are both positive, is x greater than 4?

(1) x > y
(2) In the coordinate plane, the point (x, y) lies outside a circle of radius 5 centered at the origin.

Kudos for a correct solution.

From the stem we know x > 0 and y > 0

(1) Clearly not sufficient. X = 2, y = 1 works and so does x = 5, y = 4 (although we are not limited to integers as in the choices I made)

(2) we now know x^2+y^2 > 25, and x > 0, y > 0 This is still not sufficient. Examples include x = 1, y = 100 and x = 6, y = 2

(+) now in the coordinate plane, we only care about points in quadrant one that are both below the line y=x in and outside the circle y^2+x^2 = 25

It is obvious that we can find values of x that satisfy this >4, so the question is are there any values of 4 or less. Well the minimum value has to be just greater than 2x^2 = 25 (subbing in y=x for y in the equation of the circle). That gives us the square root of 12.5 which is less than the square of 4 (16), so x could be less than or equal to 4 still. Re: If x and y are both positive, is x greater than 4?   [#permalink] 23 Oct 2018, 13:07
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# If x and y are both positive, is x greater than 4?

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