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DelSingh
If 0<x<y, is y-x < 0.00005

(1) x>1/60,000
(2) y<1/15,000



Source: GMAT Prep question pack 1

There are two ways to deal with it.

Method 1:

Is y-x < 0.00005?

We can see that both statements alone are not sufficient.

(1) x>1/60,000
(2) y<1/15,000

We know that we can add inequalities when they have the same sign ie.
a < b
c < d
then, a+c < b+d

Also, when we multiply an inequality by -1, the inequality sign flips.
x>1/60,000 implies -x < -1/60,000

You can add these two inequalities: -x < -1/60,000 and y<1/15,000 to get y-x < 1/15000 - 1/60,000
which is y-x < 1/20,000 i.e. y-x < 0.00005

Another method is to see this on the number line. Draw a number line to understand this.

0<x<y implies that x and y are both positive and x is to the left of y on the number line.
Is y-x < 0.00005 means is the distance between x and y less than .00005?

(1) x>1/60,000
means x lies to the right of 1/60,000

(2) y<1/15,000
means y lies to the left of 4/60,000

So the distance between them must be less than 4/60,000 - 1/60,000 = 3/60,000 = .00005
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(1) Insufficient. We know nothing about \(y\).
(2) Insufficient. We know nothing about \(x\).

(1)+(2) Sufficient.
We know that \(y<\frac{1}{15,000}\) and \(-x<-\frac{1}{60,000}\). If we add this two inequalities we will get:
\(y-x<\frac{1}{15,000}-\frac{1}{60,000}=\frac{1}{20,000}=0.00005\)


The correct answer is C.
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Bunuel
If 0<x<y, is y-x < 0.00005

Notice that \(0.00005=\frac{5}{100,000}=\frac{3}{60,000}\), and \(\frac{1}{15,000}=\frac{4}{60,000}\).


So, we can rewrite the question as:

If 0<x<y, is y-x<3

(1) x>1 --> if \(x=2\) and \(y=3\) then the answer is YES but if \(x=2\) and \(y=5\) the answer is NO. Not sufficient.
(2) y<4 --> if \(x=2\) and \(y=3\) then the answer is YES but if \(x=0.5\) and \(y=3.5\) the answer is NO. Not sufficient.

(1)+(2) Remember we can subtract inequalities if their signs are in opposite directions --> subtract (1) from (2): \(y-x<4-1\) --> \(y-x<3\). Sufficient.

Answer: C.

How do you know what sign the combined inequality takes when combining two inequalities with different signs?
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Bunuel
If 0<x<y, is y-x < 0.00005

Notice that \(0.00005=\frac{5}{100,000}=\frac{3}{60,000}\), and \(\frac{1}{15,000}=\frac{4}{60,000}\).


So, we can rewrite the question as:

If 0<x<y, is y-x<3

(1) x>1 --> if \(x=2\) and \(y=3\) then the answer is YES but if \(x=2\) and \(y=5\) the answer is NO. Not sufficient.
(2) y<4 --> if \(x=2\) and \(y=3\) then the answer is YES but if \(x=0.5\) and \(y=3.5\) the answer is NO. Not sufficient.

(1)+(2) Remember we can subtract inequalities if their signs are in opposite directions --> subtract (1) from (2): \(y-x<4-1\) --> \(y-x<3\). Sufficient.

Answer: C.

How do you know what sign the combined inequality takes when combining two inequalities with different signs?

ADDING/SUBTRACTING INEQUALITIES

1. You can only add inequalities when their signs are in the same direction:

If \(a>b\) and \(c>d\) (signs in same direction: \(>\) and \(>\)) --> \(a+c>b+d\).
Example: \(3<4\) and \(2<5\) --> \(3+2<4+5\).

2. You can only apply subtraction when their signs are in the opposite directions:

If \(a>b\) and \(c<d\) (signs in opposite direction: \(>\) and \(<\)) --> \(a-c>b-d\) (take the sign of the inequality you subtract from).
Example: \(3<4\) and \(5>1\) --> \(3-5<4-1\).

Check for more the links below:
Inequalities Made Easy!
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VeritasKarishma
DelSingh
If 0<x<y, is y-x < 0.00005

(1) x>1/60,000
(2) y<1/15,000



Source: GMAT Prep question pack 1

There are two ways to deal with it.

Method 1:

Is y-x < 0.00005?

We can see that both statements alone are not sufficient.

(1) x>1/60,000
(2) y<1/15,000

We know that we can add inequalities when they have the same sign ie.
a < b
c < d
then, a+c < b+d

Also, when we multiply an inequality by -1, the inequality sign flips.
x>1/60,000 implies -x < -1/60,000

You can add these two inequalities: -x < -1/60,000 and y<1/15,000 to get y-x < 1/15000 - 1/60,000
which is y-x < 1/20,000 i.e. y-x < 0.00005

Another method is to see this on the number line. Draw a number line to understand this.

0<x<y implies that x and y are both positive and x is to the left of y on the number line.
Is y-x < 0.00005 means is the distance between x and y less than .00005?

(1) x>1/60,000
means x lies to the right of 1/60,000

(2) y<1/15,000
means y lies to the left of 4/60,000

So the distance between them must be less than 4/60,000 - 1/60,000 = 3/60,000 = .00005


VeritasKarishma (see highlighted) can you explain highlighted / i mean why you write "y lies to the left of 4/60,000" and not "y lies to the left of 1/15,000"

x is greater than 1/60,000 so x can have many options same logic applies to Y if y<1/15,000 then can take numerous values

my question is why did you take these values to determine answer ---> 4/60,000 - 1/60,000 = 3/60,000
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VeritasKarishma
DelSingh
If 0<x<y, is y-x < 0.00005

(1) x>1/60,000
(2) y<1/15,000



Source: GMAT Prep question pack 1

There are two ways to deal with it.

Method 1:

Is y-x < 0.00005?

We can see that both statements alone are not sufficient.

(1) x>1/60,000
(2) y<1/15,000

We know that we can add inequalities when they have the same sign ie.
a < b
c < d
then, a+c < b+d

Also, when we multiply an inequality by -1, the inequality sign flips.
x>1/60,000 implies -x < -1/60,000

You can add these two inequalities: -x < -1/60,000 and y<1/15,000 to get y-x < 1/15000 - 1/60,000
which is y-x < 1/20,000 i.e. y-x < 0.00005

Another method is to see this on the number line. Draw a number line to understand this.

0<x<y implies that x and y are both positive and x is to the left of y on the number line.
Is y-x < 0.00005 means is the distance between x and y less than .00005?

(1) x>1/60,000
means x lies to the right of 1/60,000

(2) y<1/15,000
means y lies to the left of 4/60,000

So the distance between them must be less than 4/60,000 - 1/60,000 = 3/60,000 = .00005


VeritasKarishma (see highlighted) can you explain highlighted / i mean why you write "y lies to the left of 4/60,000" and not "y lies to the left of 1/15,000"

x is greater than 1/60,000 so x can have many options same logic applies to Y if y<1/15,000 then can take numerous values

my question is why did you take these values to determine answer ---> 4/60,000 - 1/60,000 = 3/60,000

dave13:
I want to make the fractions comparable and want to be able to perform operations on them. When are two fractions comparable? They are intuitive to compare and we can perform operations on them when they have the same denominator.

One fraction given is 1/60,000.

Another fraction given is 1/15,000. So I multiply and divide it by 4 to get 4/60,000. Since I multiply and divide by the same number, the fraction does not change.
1/15,000 = 4/60,000

Now I can easily perform operations on 1/60,000 and 4/60,000.
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1. What is the number line logic?

2. Also how are we subtracting the 2 statements and using the sign of the inequality it is subtracted from? What is the logic

KarishmaB
DelSingh
If 0<x<y, is y-x < 0.00005

(1) x>1/60,000
(2) y<1/15,000



Source: GMAT Prep question pack 1

There are two ways to deal with it.

Method 1:

Is y-x < 0.00005?

We can see that both statements alone are not sufficient.

(1) x>1/60,000
(2) y<1/15,000

We know that we can add inequalities when they have the same sign ie.
a < b
c < d
then, a+c < b+d

Also, when we multiply an inequality by -1, the inequality sign flips.
x>1/60,000 implies -x < -1/60,000

You can add these two inequalities: -x < -1/60,000 and y<1/15,000 to get y-x < 1/15000 - 1/60,000
which is y-x < 1/20,000 i.e. y-x < 0.00005

Another method is to see this on the number line. Draw a number line to understand this.

0<x<y implies that x and y are both positive and x is to the left of y on the number line.
Is y-x < 0.00005 means is the distance between x and y less than .00005?

(1) x>1/60,000
means x lies to the right of 1/60,000

(2) y<1/15,000
means y lies to the left of 4/60,000

So the distance between them must be less than 4/60,000 - 1/60,000 = 3/60,000 = .00005
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Elite097
1. What is the number line logic?
2. How are we subtracting the 2 statements and using the sign of the inequality it is subtracted from? What is the logic
Elite097 Draw 0, x, and y from left to right as described in the free info.
The question is about the distance between x and y. We know that y sits to the right of x, and the question is whether the distance between them is "microscopic." 0.00005 = 5/100,000 = 1/20,000. Neither statement can possibly be sufficient on its own, because we're interested in the distance between x and y. Combining the statements may be useful, as we're given a bottom limit for x and an upper limit for y, forcing the distance between them to be less than some quantity. What quantity, exactly? Well, (1/15,000 - 1/60,000). Let's expand by a factor of 60,000 and infer that y-x < 3.
Rephrase the question, expanding by the same factor of 60,000 and get: Is y-x < 3?
So the statements, combined, give us a definitive YES.
To your second question: Given two inequalities, we can reason that the sum of the bigger sides of the two inequalities must be greater than the sum of the two smaller sides of the two inequalities. If you want to subtract one inequality from the other, you can expand/reduce by a factor of (-1) the inequality that you wish to subtract (remembering to flip the sign, since the action you took flipped everything to the other side of zero, the mirror image), and then "add" the inequalities.
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Bunuel
If 0<x<y, is y-x < 0.00005

Notice that \(0.00005=\frac{5}{100,000}=\frac{3}{60,000}\), and \(\frac{1}{15,000}=\frac{4}{60,000}\).


So, we can rewrite the question as:

If 0<x<y, is y-x<3

(1) x>1 --> if \(x=2\) and \(y=3\) then the answer is YES but if \(x=2\) and \(y=5\) the answer is NO. Not sufficient.
(2) y<4 --> if \(x=2\) and \(y=3\) then the answer is YES but if \(x=0.5\) and \(y=3.5\) the answer is NO. Not sufficient.

(1)+(2) Remember we can subtract inequalities if their signs are in opposite directions --> subtract (1) from (2): \(y-x<4-1\) --> \(y-x<3\). Sufficient.

Answer: C.
­After subtracting we only got that x-y<3 but how do we know that x-y is also less than 3/60000 ?
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Bunuel
If 0<x<y, is y-x < 0.00005

Notice that \(0.00005=\frac{5}{100,000}=\frac{3}{60,000}\), and \(\frac{1}{15,000}=\frac{4}{60,000}\).


So, we can rewrite the question as:

If 0<x<y, is y-x<3

(1) x>1 --> if \(x=2\) and \(y=3\) then the answer is YES but if \(x=2\) and \(y=5\) the answer is NO. Not sufficient.
(2) y<4 --> if \(x=2\) and \(y=3\) then the answer is YES but if \(x=0.5\) and \(y=3.5\) the answer is NO. Not sufficient.

(1)+(2) Remember we can subtract inequalities if their signs are in opposite directions --> subtract (1) from (2): \(y-x<4-1\) --> \(y-x<3\). Sufficient.

Answer: C.
­After subtracting we only got that x-y<3 but how do we know that x-y is also less than 3/60000 ?
After rewrring the question we get:

If 0 < x < y, is y - x < 3?

(1) x > 1 
(2) y < 4 
So, getting y - x < 3 gives a YES anwswer to that rephrased question. 


 
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