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Is x<20 ?

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by apoorva.srivastva » Thu Jul 16, 2009 11:33 am
Is x<20 ?

1. sum of x and y is < 20
2. y is less than 20

my reasoning is as follows:

from 1 : X+Y < 20
From 2 : y<20

Subtract 2 from 1

X<0

Hence,is x<20 ? or insufficeint!!!

KIndly Help!!
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Source: — Data Sufficiency |

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by Ian Stewart » Thu Jul 16, 2009 12:00 pm
You can add two inequalities, but you can't subtract them. Take an example of two inequalities which are true, and subtract:

2 > 1
2 > 0
0 > 1

which is clearly false.

In the question above, x could be 30 and y could be -11, or x could be 10 and y could be 9, so the answer is E.
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by mike22629 » Thu Jul 16, 2009 12:02 pm
IMO E.

Just try different numbers

x = 21 y = -2

x = 19 y = 1

You can't subtract inequalities, only add them.
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by mike22629 » Thu Jul 16, 2009 12:03 pm
Oops

In second example x would have to be 18 so x + y is less than 20, but you get the point.
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by tohellandback » Thu Jul 16, 2009 12:30 pm
Ian Stewart wrote:You can add two inequalities, but you can't subtract them. Take an example of two inequalities which are true, and subtract:

2 > 1
2 > 0
0 > 1

which is clearly false.

In the question above, x could be 30 and y could be -11, or x could be 10 and y could be 9, so the answer is E.
Just adding something to it.
You can always subtract a constant from the both sides of an equality.
The powers of two are bloody impolite!!
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by apoorva.srivastva » Thu Jul 16, 2009 9:17 pm
[quote="Ian Stewart"][b]You can add two inequalities, but you can't subtract them. Take an example of two inequalities which are true, and subtract:[/b]
2 > 1
[u]2 > 0 [/u]
0 > 1

which is clearly false.

In the question above, x could be 30 and y could be -11, or x could be 10 and y could be 9, so the answer is E.[/quote]

Thanks Ian and Mike for pointing it to me...Inequalities always come up with revelations.....
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