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Bunuel
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A computer program selects integers to populate a data bank according 27 Dec 2016, 09:04
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A
Be sure to select an answer first to save it in the Error Log before revealing the correct answer (OA)!

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75% (hard)

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42% (01:58) correct 58% (02:07) wrong based on 69 sessions

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A computer program selects integers to populate a data bank according to the following conditions:

I. If a is in the data bank then -a is in the data bank
II. If a and b are in the data bank than ab is selected for the data bank.
III. If ab is in the data bank than a and b are selected for the data bank.

Is –6 in the data bank?

(1) c, which is an even multiple of 15, is in the bank.
(2) the prime factors of c are in the data bank.
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A
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A computer program selects integers to populate a data bank according 27 Dec 2016, 21:42
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St1: c, which is an even multiple of 15, is in the bank. --> Say c = 15*2 = 30
30 = 5 * 6
If 5 and 6 are there in the data bank then -5 and -6 are in the data bank.
Sufficient

St2: the prime factors of c are in the data bank. - Clearly insufficient.

Answer: A
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A computer program selects integers to populate a data bank according 30 Dec 2016, 04:41
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answer should be E
if we take c=0 which is even multiple of 15 and hence -6 is not in the data bank, and statement 2 does not provide any info. about c so insuff. now combine both we still can't say -6 is in data bank or not so answer shold be E .

correct me if m wrong!
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A computer program selects integers to populate a data bank according 30 Dec 2016, 06:12
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Vyshak
St1: c, which is an even multiple of 15, is in the bank. --> Say c = 15*2 = 30
30 = 5 * 6
If 5 and 6 are there in the data bank then -5 and -6 are in the data bank.
Sufficient

St2: the prime factors of c are in the data bank. - Clearly insufficient.

Answer: A

Hi Vyshak,

I've a question.
30=30*1 too right? Now, we don't know clearly if -6 is in the bank.

If cond 2 is also considered, prime factors of 30=2*3*5.
2 & 3 are in the bank, so 2*3=6 is in the bank (coz, II.) Therefore -6 is in the bank (coz, III.)

So the answer must be C, am I missing something?

nks2611 your point is valid too mate! Nice. Thanks :)
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A computer program selects integers to populate a data bank according 30 Dec 2016, 07:20
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Is my answer right? Sirakri

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A computer program selects integers to populate a data bank according 30 Dec 2016, 09:40
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Sirakri
Vyshak
St1: c, which is an even multiple of 15, is in the bank. --> Say c = 15*2 = 30
30 = 5 * 6
If 5 and 6 are there in the data bank then -5 and -6 are in the data bank.
Sufficient

St2: the prime factors of c are in the data bank. - Clearly insufficient.

Answer: A

Hi Vyshak,

I've a question.
30=30*1 too right? Now, we don't know clearly if -6 is in the bank.

If cond 2 is also considered, prime factors of 30=2*3*5.
2 & 3 are in the bank, so 2*3=6 is in the bank (coz, II.) Therefore -6 is in the bank (coz, III.)

So the answer must be C, am I missing something?

nks2611 your point is valid too mate! Nice. Thanks :)

Hi Sirakri,

We just have to find the factors of 30 here. They need not be prime factors. If 30 is there in the dataset then its implied that 1, 2, 3, 5, 6, 10 and 15 are there in the dataset. And, we will have corresponding negative values too. Also, the dataset is not limited to the mentioned values as each value gives rise to many different values. Since 6 is one of the factors of 30, we can be sure that -6 will also be in the dataset.
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A computer program selects integers to populate a data bank according 30 Dec 2016, 14:03
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Vyshak
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St1: c, which is an even multiple of 15, is in the bank. --> Say c = 15*2 = 30
30 = 5 * 6
If 5 and 6 are there in the data bank then -5 and -6 are in the data bank.
Sufficient

St2: the prime factors of c are in the data bank. - Clearly insufficient.

Answer: A

Hi Vyshak,

I've a question.
30=30*1 too right? Now, we don't know clearly if -6 is in the bank.

If cond 2 is also considered, prime factors of 30=2*3*5.
2 & 3 are in the bank, so 2*3=6 is in the bank (coz, II.) Therefore -6 is in the bank (coz, III.)

So the answer must be C, am I missing something?

nks2611 your point is valid too mate! Nice. Thanks :)

Hi Sirakri,

We just have to find the factors of 30 here. They need not be prime factors. If 30 is there in the dataset then its implied that 1, 2, 3, 5, 6, 10 and 15 are there in the dataset. And, we will have corresponding negative values too. Also, the dataset is not limited to the mentioned values as each value gives rise to many different values. Since 6 is one of the factors of 30, we can be sure that -6 will also be in the dataset.

Hi Vyshak,

Thanks for the explanation. I'm learning the logic, thanks again :)
Then how do we comply with nks2611's explanation here? Any idea? Thanks in advance.

nks2611 I'm no expert mate, I don't know just yet haha! I'm learning as we speak.
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A computer program selects integers to populate a data bank according 31 Dec 2016, 06:34
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Sirakri
Hi Vyshak,

Thanks for the explanation. I'm learning the logic, thanks again :)
Then how do we comply with nks2611's explanation here? Any idea? Thanks in advance.

c = 0, 30, 60, 90, ...... --> All the values are present in the dataset.
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A computer program selects integers to populate a data bank according 14 Jan 2017, 02:43
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Bunuel
A computer program selects integers to populate a data bank according to the following conditions:

I. If a is in the data bank then -a is in the data bank
II. If a and b are in the data bank than ab is selected for the data bank.
III. If ab is in the data bank than a and b are selected for the data bank.

Is –6 in the data bank?

(1) c, which is an even multiple of 15, is in the bank.
(2) the prime factors of c are in the data bank.

Although I also marked C but after careful anaylysis I think the approach should be as under:
State 1) even multiple of 15 us there, i.e. 2 is there and 15 is there, or -2 is there and -15 is there. Now coz ab is in data bank i.e.15 is in data bank, 2,3,-2,-3,1,-1 are in data bank or now we have a lot of numbers in data bank 1,-1,2,-2,3,-3,6,-6,15,-15 etc and so on.Fro statement II of given conditions....all the combinations of such numbers will be in data bank....and -6 is one them...THEREFORE STATE 1 IS SUFFICINT..
STATEMENT 2)well no need to say that it is there just coz there r to be 2 statements....nothing is coming out of it--Insuff.


Good Question I would say...
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A computer program selects integers to populate a data bank according 15 Oct 2019, 12:50
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Bunuel
A computer program selects integers to populate a data bank according to the following conditions:

I. If a is in the data bank then -a is in the data bank
II. If a and b are in the data bank than ab is selected for the data bank.
III. If ab is in the data bank than a and b are selected for the data bank.

Is –6 in the data bank?

(1) c, which is an even multiple of 15, is in the bank.
(2) the prime factors of c are in the data bank.


by understanding that statement 3 tells us that all factors yielding ab will be contained in the data bank the problem becomes a cakewalk

ex: 25 is in the data, then 5*5=25 hence 5 is in the data bank.

Statement 1: c could be 30, 60, 90..... in all these numbers 6 is present and hence -6 is present

Sufficient

Statement 2 clearly is insufficient.

Hence A
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A computer program selects integers to populate a data bank according 15 Oct 2019, 19:47
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I get why A is the answer though I got it wrong and marked C.
A. c, which is an even multiple of 15, is in the bank.-
Since sentence III "If ab is in the data bank than a and b are selected for the data bank, clearly states AB."
We are free to assume ab for 30 to be 30 X 1, 15 x 2, 5 x 6 (in which case -6 would be present).
However, this question is a little vague and will not be asked in this exact format on the GMAT. It is still good as a question as GMAT does give questions that require us to follow such steps.
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