Is Q a prime number? : GMAT Data Sufficiency (DS)
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Is Q a prime number?

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Is Q a prime number? [#permalink]

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New post 17 Jun 2010, 03:32
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Q is less than 10. Is Q a prime number?

(1) Q^2 - 2 = P; P is prime and P < 10.
(2) Q + 2 is NOT prime, but Q is a positive integer.
[Reveal] Spoiler: OA

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Re: Is Q a prime number? [#permalink]

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New post 17 Jun 2010, 05:26
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ykaiim wrote:
Q is less than 10. Is Q a prime number?

1) \(Q^2\) - 2 = P; P is prime and P < 10.
2) Q + 2 is NOT prime, but Q is a positive integer.


Given: \(q<10\). Question: \(q=prime\)?

(1) \(q^2-2=p=prime<10\) --> if \(p=7\), then \(q=3=prime\) or \(q=-3\neq{prime}\). Not sufficient.

(2) \(q+2\neq{prime}\), \(q=positive \ integer\). If \(q=2\) then answer is YES but if \(q=4\), then answer is NO. Not sufficient. From this statement \(q\) can take the following values: 2, 4, 6, 7, 8 (remember \(q<10\) and \(q+2\neq{prime}\)).

(1)+(2) The only value from (2) that satisfies \(q^2-2=prime<10\) is when \(q=2=prime\). Sufficient.

Answer: C.
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Re: Is Q a prime number? [#permalink]

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New post 17 Jun 2010, 06:32
Thanks Bunuel. This confirmed my reasoning.
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Re: Is Q a prime number? [#permalink]

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New post 05 Jan 2017, 09:31
Bunuel wrote:
ykaiim wrote:
Q is less than 10. Is Q a prime number?

1) \(Q^2\) - 2 = P; P is prime and P < 10.
2) Q + 2 is NOT prime, but Q is a positive integer.


Given: \(q<10\). Question: \(q=prime\)?

(1) \(q^2-2=p=prime<10\) --> if \(p=7\), then \(q=3=prime\) or \(q=-3\neq{prime}\). Not sufficient.

(2) \(q+2\neq{prime}\), \(q=positive \ integer\). If \(q=2\) then answer is YES but if \(q=4\), then answer is NO. Not sufficient. From this statement \(q\) can take the following values: 2, 4, 6, 7, 8 (remember \(q<10\) and \(q+2\neq{prime}\)).

(1)+(2) The only value from (2) that satisfies \(q^2-2=prime<10\) is when \(q=2=prime\). Sufficient.

Answer: C.



"if \(q=4\), then answer is NO". Is it correct or typing error?
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Re: Is Q a prime number? [#permalink]

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New post 05 Jan 2017, 09:36
Mahmud6 wrote:
Bunuel wrote:
ykaiim wrote:
Q is less than 10. Is Q a prime number?

1) \(Q^2\) - 2 = P; P is prime and P < 10.
2) Q + 2 is NOT prime, but Q is a positive integer.


Given: \(q<10\). Question: \(q=prime\)?

(1) \(q^2-2=p=prime<10\) --> if \(p=7\), then \(q=3=prime\) or \(q=-3\neq{prime}\). Not sufficient.

(2) \(q+2\neq{prime}\), \(q=positive \ integer\). If \(q=2\) then answer is YES but if \(q=4\), then answer is NO. Not sufficient. From this statement \(q\) can take the following values: 2, 4, 6, 7, 8 (remember \(q<10\) and \(q+2\neq{prime}\)).

(1)+(2) The only value from (2) that satisfies \(q^2-2=prime<10\) is when \(q=2=prime\). Sufficient.

Answer: C.



"if \(q=4\), then answer is NO". Is it correct or typing error?


Why do you think it's an error? 4 + 2 = 6, which is not a prime, so the second statement is satisfied and 4 is not a prime, so the answer to the question whether q is a prime is no.
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Resources:
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Collection of Questions:
PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat

DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.


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Kudos [?]: 23 [0], given: 90

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Re: Is Q a prime number? [#permalink]

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New post 05 Jan 2017, 09:55
Sorry, Bunuel.
My thought went in different ways, that's why I could not get it. You are right. Thanks.
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Re: Is Q a prime number?   [#permalink] 05 Jan 2017, 09:55
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