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value of mod(x+7)

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value of mod(x+7)

by gibran » Mon May 19, 2008 10:11 am
What is the value of |x + 7| =?
(1) |x + 3|= 14
(2) (x + 2)^2 = 169
A. Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient.
B. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient.
C. BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient.
D. EACH statement ALONE is sufficient.
E. Statements (1) and (2) TOGETHER are NOT sufficient.

IMO, it is E. But OA says it is D

From (1), we get x = -17 or x=11. Not SUFF
From (2), (x+2)^2=169 gives x=11 and x=-13. Not Suff.

Taking (1) and (2) together, we cannot determine the value of x. Hence E.

Somebody please tell me if I am doing something wrong?
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by punit.kaur.mba » Mon May 19, 2008 12:57 pm
I would go with E too.
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by nikhilc_1 » Mon May 19, 2008 1:26 pm
I think you are right. Its has to be E.
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by sxjain3 » Mon May 19, 2008 2:24 pm
the answer is C, as from 2 conditions, we can arrive at a common value for x which is 11.

Per the rules, the 2 conditions will not contradict each other and as the unique value of x as 11 satisfies the 2 conditions, we can say that the value of x is 11 and hence the question can be answered.
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by mim3 » Mon May 19, 2008 2:45 pm
sxjain3 wrote:the answer is C, as from 2 conditions, we can arrive at a common value for x which is 11.

Per the rules, the 2 conditions will not contradict each other and as the unique value of x as 11 satisfies the 2 conditions, we can say that the value of x is 11 and hence the question can be answered.
Agreed, it's C. For value DS questions when neither statement is sufficient, circle the values that hold for each statement. If there's only one common value, that's your answer. Here, it's 11.
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by netigen » Mon May 19, 2008 3:14 pm
from A

x=11 or x=-17

from B

x=11 or x=-15

hence C
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by punit.kaur.mba » Tue May 20, 2008 8:02 am
I did not know that ... Thanks for the tip! Could you tell me a book that is good for such DS strategies?
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by chidcguy » Tue May 20, 2008 5:02 pm
Also, to add

if

(1) says X=11/-17/-13

(2) says X=11/-13

Ans is E

if

(1) says X=11/-17/-13

(2) says X=11

Ans is B
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by sriraj » Wed May 21, 2008 4:42 am
What is the value of |x + 7| =?
(1) |x + 3|= 14
(2) (x + 2)^2 = 169


I presume answer is D.
Since question is to find |x+7| and not value of x.
Given |x+3| = 14, we can find |x+7| as 18.

simialrly
(x + 2)^2 = 169 == > x+2 = plus or minus 13
i.e |x+2| = 13
given |x+2| =13, |x+7| = 13+5 = 18.

So each option is alone sufficient, since question is to find |x+7| and not x
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by gabriel » Wed May 21, 2008 7:27 am
sriraj wrote:What is the value of |x + 7| =?
(1) |x + 3|= 14
(2) (x + 2)^2 = 169


I presume answer is D.
Since question is to find |x+7| and not value of x.
Given |x+3| = 14, we can find |x+7| as 18.

simialrly
(x + 2)^2 = 169 == > x+2 = plus or minus 13
i.e |x+2| = 13
given |x+2| =13, |x+7| = 13+5 = 18.

So each option is alone sufficient, since question is to find |x+7| and not x
This is wrong. Remember if |x+3| = 14 that means (x+3) could be equal to 14 or -14 so (x+7) could be equal to 18 or -10. Same goes for your second statement.

I completely agree with netigen, the answer is C.
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It is right..

by sriraj » Wed May 21, 2008 7:34 am
Hey,
As per my explantion.. question is not x+7 the question is also mod(x+7)

if mod(x+3) = 14 ..definitely mod(x+7) = 18.
Similarly for my second argument. hope this clarifies
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Re: It is right..

by gabriel » Wed May 21, 2008 10:15 am
sriraj wrote:Hey,
As per my explantion.. question is not x+7 the question is also mod(x+7)

if mod(x+3) = 14 ..definitely mod(x+7) = 18.
Similarly for my second argument. hope this clarifies
Sriraj, you are missing some very important basics about Modulus in your solution.

Remember (|x+3|+4) is not equal to |x+7|. |x+7| = |(x+3)+4|, that is 4 is inside the modulus and this fact changes the whole solution.

Try substituting numbers for x and you will see where you are going wrong.

Regards.
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by sriraj » Wed May 21, 2008 11:01 am
Agree,
|x+p| not equal to |x| +p
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by mim3 » Fri May 23, 2008 9:17 am
punit.kaur.mba wrote:I did not know that ... Thanks for the tip! Could you tell me a book that is good for such DS strategies?
Punit- I picked it up from Manhattan GMAT, but I think any of the major prep companies would use that or similar approaches.
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by airan » Sun Jun 01, 2008 1:05 am
So what is the final answer here ?
And how do we deal with such issues where we have difference in understanding ....!
Thanks
Airan
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