a + b > - c

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maihuna
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Topic: a + b > - c
PostFri Oct 30, 2009 9:54 am Reply with quote
If a + b > - c, is a > 2?

(1) a + b + c > 8
(2) - a + b + c < - 4


This is a yes/no question so you should plug in. For statement 1, if you plug in a = 3, b = 5, c = 4, then you get an answer of “yes,” but if a = 1, b = 6, c = 2, then you get an answer of “no,” so you should write down BCE. Now try plugging in for statement 2. Remember, when you’re plugging into a yes/no question that begins “If . . .”, you have to find numbers that satisfy both the statement and the “If” part of the question. So if a = 3 and b = 2, then c could be " 4 and you get an answer of “yes.” Go ahead and try to get an answer of no. If a = 2 and b = 2, then, according to the original “If” constraint, c has to be greater than " 4. But " 2 + 2 + " 3.9 = " 3.9, which is greater than " 4. No matter what number for a < 2 you try to plug in, it won’t satisfy both the statement and the constraint. Therefore, the answer has to be B.


Any better explanation possible, i thought of this one:
Given a+b+c>0 1 says the same thing, 2 says :
a>-b-c, using 2, -a < -b-c-4 or a>b+c+4
adding the two: 2a>4 or a>2

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alexchow
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PostSun Nov 01, 2009 5:41 am Reply with quote
Looks like b.

(i) means a+b-8>-c but composition of a+b is not known.

(ii) subtract the inequalities

a+b > -c
-
-a+b > -4 -c
=
a-(-a)+b-b > -c-(-4-c)

--> 2a >4 ---> a>2

Sufficient.
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satish.nagdev
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PostSun Nov 01, 2009 10:31 am Reply with quote
IMO C,
we need both statements to determine a's value.
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PostMon Nov 02, 2009 9:08 am Reply with quote
satish.nagdev wrote:
IMO C,
we need both statements to determine a's value.
can u please explain
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satish.nagdev
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PostMon Nov 02, 2009 7:33 pm Reply with quote
I approached in this way

given
1) a + b + c > 8 ==> no info about a
2) - a + b + c < - 4 ==> no info about a

together

(1) a + b + c > 8
(2) - a + b + c < - 4 ==> a -b -c >4
a + b + c + a - b - c > 8 + 4
2a > 12
a > 6
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PostMon Nov 02, 2009 8:04 pm Reply with quote
IMO - C

Solution - same as above
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2010gmat
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PostTue Nov 03, 2009 1:50 am Reply with quote
maihuna...i agree with you..ans should be B
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crackgmat007
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PostTue Nov 03, 2009 1:32 pm Reply with quote
1. Not sufficient - as it says a + b + c > 8

2. Sufficient - add inequalities given in question

a + b + c > 0

a - b - c > 4 ( multiply stmt 2 with with -1)

We get a > 2
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PostTue Nov 03, 2009 2:29 pm Reply with quote
satish.nagdev wrote:
I approached in this way

given
1) a + b + c > 8 ==> no info about a
2) - a + b + c < - 4 ==> no info about a

together

(1) a + b + c > 8
(2) - a + b + c < - 4 ==> a -b -c >4
a + b + c + a - b - c > 8 + 4
2a > 12
a > 6
The reason why you incorrectly arrive at "C" is because you're ignoring the original inequality:

a + b + c > 0

You can do the exact same thing with statement (2) alone and the original inequality as you did when combining the two statements. Since we have that original inequality, we don't need statement (1) at all.

Remember step 2 of the Kaplan Method for DS:

look at each statement individually, in conjunction with the information in the question stem.

Since (2) + the orginal information is sufficient, (B) is the correct answer to the question.
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PostTue Nov 03, 2009 5:51 pm Reply with quote
Thanks Stuart for correcting
when will I quit these silly mistakes Sad( Sad
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