Is x less than 20? : GMAT Data Sufficiency (DS)
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# Is x less than 20?

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Is x less than 20? [#permalink]

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20 Mar 2012, 08:07
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Is x less than 20?

(1) The sum of x and y is less than 20.
(2) y is less than 20.
[Reveal] Spoiler: OA

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Re: Is x less than 20? [#permalink]

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20 Mar 2012, 08:17
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enigma123 wrote:
Is x < 20?

1. Sum of x and y is less than 20

2. y is less than 20

How come the answer is E and not A?

Consider two cases:
x=30 and y=-15;
x=15 and y=-15;

Both examples satisfy the statements and give different answers to the question whether x<20. Not sufficient.

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Is x less than 20? [#permalink]

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04 Feb 2014, 20:56
nfa1rhp wrote:
Is x less than 20?

1) The sum of x and y is less than 20

2) y is less than 20

I thought working together they would be sufficient but they are not.
[/quote]

Ans E

1 & 2 not sufficient : as difference of two numbers does not implicate their magnitude in any way
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Re: Is x less than 20? [#permalink]

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01 Mar 2014, 13:16
but if we solve it like this:
subtract
x+y < 20
y < 20

x+y-y<0
x<0

then x will be certainly less than 20...

Why is this approach flawed ?

Bunuel wrote:
enigma123 wrote:
Is x < 20?

1. Sum of x and y is less than 20

2. y is less than 20

How come the answer is E and not A?

Consider two cases:
x=30 and y=-15;
x=15 and y=-15;

Both examples satisfy the statements and give different answers to the question whether x<20. Not sufficient.

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Re: Is x less than 20? [#permalink]

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02 Mar 2014, 03:20
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mariofelix wrote:
but if we solve it like this:
subtract
x+y < 20
y < 20

x+y-y<0
x<0

then x will be certainly less than 20...

Why is this approach flawed ?

Bunuel wrote:
enigma123 wrote:
Is x < 20?

1. Sum of x and y is less than 20

2. y is less than 20

How come the answer is E and not A?

Consider two cases:
x=30 and y=-15;
x=15 and y=-15;

Both examples satisfy the statements and give different answers to the question whether x<20. Not sufficient.

That's wrong because you cannot subtract inequalities with signs in the same direction.

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 $$2<5$$ --> $$3+2<4+5$$.

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 $$5>1$$ --> $$3-5<4-1$$.

Hope it helps.
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21 Jul 2014, 15:55
Hi All,

I have a question regarding a data sufficiency problem.

Is x less than 20?

1) x + y < 20
2) y is less than 20

My question refers to 1.). In this case, since it says x + y, can we plug in a negative number in for y even with a + sign in front of it?

ex. if x=25, y=-8,
25 + (-8) = 17
we do not know if x<20, therefore INSUFFICIENT

I am sure this question is pretty basic to most, but it is these small details that seem to throw me off while solving DS problems. Any advice would be very helpful.

BTW - This question is from the CAT on GMATPrep software.

Thanks,
Mike
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Re: Is x less than 20? [#permalink]

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22 Jul 2014, 02:24
MikeA2606 wrote:
Hi All,

I have a question regarding a data sufficiency problem.

Is x less than 20?

1) x + y < 20
2) y is less than 20

My question refers to 1.). In this case, since it says x + y, can we plug in a negative number in for y even with a + sign in front of it?

ex. if x=25, y=-8,
25 + (-8) = 17
we do not know if x<20, therefore INSUFFICIENT

I am sure this question is pretty basic to most, but it is these small details that seem to throw me off while solving DS problems. Any advice would be very helpful.

BTW - This question is from the CAT on GMATPrep software.

Thanks,
Mike

Merging similar topics. Please refer to the discussion above.

As for your question: y is some number, it could be negative, positive or 0. So, you can plug any number you want there.

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Re: Is x less than 20? [#permalink]

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13 Nov 2015, 04:41
For people like me who like equations (especially under time pressure of the GMAT)

For C=>

Just add 1 + 2 (same sign) to get:
x + 2y < 40
x < 40 - 2y

Its then clear x can be any number - depending on y - and less/more than 20... So E.

Further (not needed but why not), the range of x would be:
x > 2y -40
x > 2(20) -40 ( y < 20, so max y ~ 20)
x > 0
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27 May 2016, 19:27
rahsin wrote:
Is x less than 20 ?

1. The sum of x and y is less than 20.

2. y is less than 20.

Statement 1

x+y<20

say x=5, y=14, sum is 19. so x+y < 20. Also x is less than 20.

Now take x=25, y=-16, sum is 9. so x+y < 20. BUT x is more than 20.

So not sufficient

Statement 2
This statement does not say anything about x. Clearly Not sufficient.

Combining Statements 1 and 2

Our above examples will suit the purpose, as in both cases y is less than 20.

say x=5, y=14, sum is 19. so x+y < 20. Also y is less than 20. Here x is less than 20
Now take x=25, y=-16, sum is 9. so x+y < 20. Also y < 20. BUT x is more than 20.

So even after combining Not sufficient.

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13 Jul 2016, 12:17
Is x less than 20 ?
(1) The sum of x and y is less than 20.
(2) y is less than 20.

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13 Jul 2016, 13:04
Is x less than 20 ?
(1) The sum of x and y is less than 20.
(2) y is less than 20.

Solution:

Answer should be E. Here it is how:

1: x+y < 20 ---> tells us nothing about y or x. say x=24, y= -10 then x < 20 No. Say x = 17 y =1 then x <20 Yes. --- > Insufficient.
2: y <20 , nothing is told about x. ----> clearly insufficient.

Combined.
x+y < 20 and y <20. Again, use the example given in statement 1. If x=24, y= -10 then x < 20 No. If x = 17, y =1 then x <20 Yes.

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Re: Is x less than 20? [#permalink]

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13 Jul 2016, 20:24
rraghun wrote:
Is x less than 20 ?
(1) The sum of x and y is less than 20.
(2) y is less than 20.

Merging similar topics. Please refer to the discussion above.

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Re: Is x less than 20? [#permalink]

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16 Jul 2016, 12:02
rraghun wrote:
Is x less than 20 ?
(1) The sum of x and y is less than 20.
(2) y is less than 20.

Required: Is x < 20?
Statement 1: x + y < 20
Case 1: x = 1, y = 18
Case 2: x = 21, y = -29
Nothing can be said about x
INSUFFICIENT

Statement 2: y < 20
This does not give us anything about x
INSUFFICIENT

Combining both statements: x + y < 20 and y < 20
Case 1: x = 21, y = -2
Case 2: x = 18, y = 1
Still nothing can be said about x
INSUFFICIENT

Correct Option: E

Does this help?
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Re: Is x less than 20? [#permalink]

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17 Jul 2016, 22:50
enigma123 wrote:
Is x less than 20?

(1) The sum of x and y is less than 20.
(2) y is less than 20.

(1) The sum of x and y is less than 20.
x+y<20 ; infinite possible values of x ; NOT SUFFICIENT

(2) y is less than 20
Doesn't even talk about x; NOT SUFFICIENT

MERGING
x+less than 20<20
Case 1 ) Y is negative
x+(-30)<20 ==> x<50 {{{ Is x less than 20? = NO}}}

Case 1 ) Y is Positive
x+14<20 ==> x<6 {{{Is x less than 20? =YES}}}

NOT SUFFICIENT

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Re: Is x less than 20?   [#permalink] 17 Jul 2016, 22:50
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