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Question about problem 89 from OG 11 (page 285)

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by gmattic » Sat Sep 26, 2009 12:54 pm
This question asks if the following equation is valid:
k _ (l + m) = (k _ l) + (k _ m)

where _ can be one of the following operations:
+, -, x (ie: addition, subtraction, or multiplication)

the statements are :
(1) k _ 1 != 1 _ k for some k
(2) _ represents subtraction

The answer is 'D' because it claims 'subraction' is the operation.

I don't understand why since
k - (l + m) does NOT equal (k - l) + (k - m)

Is this an error in the book or am I missing something?

Thanks
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Source: — Data Sufficiency |

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Re: Question about problem 89 from OG 11 (page 285)

by Brent@GMATPrepNow » Sat Sep 26, 2009 1:13 pm
gmattic wrote:This question asks if the following equation is valid:
k _ (l + m) = (k _ l) + (k _ m)

where _ can be one of the following operations:
+, -, x (ie: addition, subtraction, or multiplication)

the statements are :
(1) k _ 1 != 1 _ k for some k
(2) _ represents subtraction

The answer is 'D' because it claims 'subraction' is the operation.

I don't understand why since
k - (l + m) does NOT equal (k - l) + (k - m)

Is this an error in the book or am I missing something?

Thanks
Keep in mind that the over-reaching question here is "Do we have enough information to determine whether we can answer the question "Is the equation k _ (l + m) = (k _ l) + (k _ m) valid?"

(2) If the operation is subtraction then the equation is NOT valid.
So, using the information in statement (2), we have definitively answered the question "Is the equation k _ (l + m) = (k _ l) + (k _ m) valid?" The answer to this question is a resounding no.
So, statement (2) is sufficient
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by glorydefined » Sat Sep 26, 2009 2:44 pm
Hi,

This ones pretty simple, the question asks if the following eq is valid :

k _ (l + m) = (k _ l) + (k _ m)

for the above eq to be valid "_" should be multiplicaiton. so basically the question is asking whether "_" is multiplication or not.

stmt 1: k _ 1 != 1 _ k for some k

this statement says "_" is subtraction. (only then the above eq will be valid). So it answers our main question, which is "k _ (l + m) = (k _ l) + (k _ m)" is invalid. Hence SUFFCIENT

stamt 2: _ represents subtraction

this statement also says the same thing. Which makes the main question invalid. Hence SUFFCIENT.

ANSWER D
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Re: Question about problem 89 from OG 11 (page 285)

by Brent@GMATPrepNow » Sat Sep 26, 2009 3:17 pm
gmattic wrote:This question asks if the following equation is valid:
k _ (l + m) = (k _ l) + (k _ m)

where _ can be one of the following operations:
+, -, x (ie: addition, subtraction, or multiplication)

the statements are :
(1) k _ 1 != 1 _ k for some k
(2) _ represents subtraction

The answer is 'D' because it claims 'subraction' is the operation.

I don't understand why since
k - (l + m) does NOT equal (k - l) + (k - m)

Is this an error in the book or am I missing something?

Thanks
I didn't comment on statement (1) because I wasn't sure what != means.
If this is just a typo and statement (1) is meant to read k _ 1 = 1 _ k for some k then _ could be any of the 4 operations when k=1.

What is the original wording of the question?
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Re: Question about problem 89 from OG 11 (page 285)

by gmattic » Sat Sep 26, 2009 10:22 pm
Brent Hanneson wrote:
gmattic wrote:This question asks if the following equation is valid:
k _ (l + m) = (k _ l) + (k _ m)

where _ can be one of the following operations:
+, -, x (ie: addition, subtraction, or multiplication)

the statements are :
(1) k _ 1 != 1 _ k for some k
(2) _ represents subtraction

The answer is 'D' because it claims 'subraction' is the operation.

I don't understand why since
k - (l + m) does NOT equal (k - l) + (k - m)

Is this an error in the book or am I missing something?

Thanks
I didn't comment on statement (1) because I wasn't sure what != means.
If this is just a typo and statement (1) is meant to read k _ 1 = 1 _ k for some k then _ could be any of the 4 operations when k=1.

What is the original wording of the question?
!= means 'does not equal'. Sorry for the confusion, its how you denote 'does not equal' in programming.

Thanks for the answer folks.
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