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If p is a positive integer, is p prime?

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Manager
Joined: 23 Sep 2016
Posts: 233
If p is a positive integer, is p prime?  [#permalink]

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19 Mar 2018, 22:32
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65% (hard)

Question Stats:

48% (01:33) correct 52% (01:45) wrong based on 69 sessions

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If p is a positive integer, is p prime?
1. The highest common factor of P and 110 is 11.
2. The least common multiple of P and 110 is 110
Current Student
Joined: 07 Jan 2016
Posts: 1088
Location: India
GMAT 1: 710 Q49 V36
Re: If p is a positive integer, is p prime?  [#permalink]

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19 Mar 2018, 23:42
rishabhmishra wrote:
If p is a positive integer, is p prime?
1. The highest common factor of P and 110 is 11.
2. The least common factor of P and 110 is 110

is the question correct?

acc to B

if 110 is the least common factor

p and 110 are multiples of 110
so p can never b prime
Director
Joined: 20 Sep 2016
Posts: 634
Location: India
Concentration: Strategy, Operations
GPA: 3.95
WE: Operations (Real Estate)
Re: If p is a positive integer, is p prime?  [#permalink]

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20 Mar 2018, 00:04
2
rishabhmishra wrote:
If p is a positive integer, is p prime?
1. The highest common factor of P and 110 is 11.
2. The least common factor of P and 110 is 110

IMO C

St. 1 not sufficient - HCF is 11 which means that there has to be a 11 in P so P could be 11 and the answer would be yes. But if P is 143 ( 11*13) the HCF is still 11 but here P is not a prime no.

St. 2 Not sufficient. LCM is 110. And the other number is 110 therefore we can conclude that either P is 110 or less than 110. Now LCM = 110= ( 11*5*2) . another number 110= 11*5*2. Now P could be either 11 or 2 or 5 or 55 or 22 or 110. As for LCM we only choose the highest power of prime no.s P cannot have more than 1 ( 11 5 2). There P could be just 11 or 5 or 2 ( prime no.s) or it could be 22 55 10 110 ( non primes)

St. 1 and St. 2 -- HCF * LCM= P* 110 ( standard formula)
Therefore- 11*110= P* 110
Therefore P is 11 ( prime no.) . C is the right answer

Sent from my XT1562 using GMAT Club Forum mobile app
Current Student
Joined: 07 Jan 2016
Posts: 1088
Location: India
GMAT 1: 710 Q49 V36
Re: If p is a positive integer, is p prime?  [#permalink]

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20 Mar 2018, 00:07
1
rishabhmishra wrote:
If p is a positive integer, is p prime?
1. The highest common factor of P and 110 is 11.
2. The least common factor of P and 110 is 110

IMO C

St. 1 not sufficient - HCF is 11 which means that there has to be a 11 in P so P could be 11 and the answer would be yes. But if P is 143 ( 11*13) the HCF is still 11 but here P is not a prime no.

St. 2 Not sufficient. LCM is 110. And the other number is 110 therefore we can conclude that either P is 110 or less than 110. Now LCM = 110= ( 11*5*2) . another number 110= 11*5*2. Now P could be either 11 or 2 or 5 or 55 or 22 or 110. As for LCM we only choose the highest power of prime no.s P cannot have more than 1 ( 11 5 2). There P could be just 11 or 5 or 2 ( prime no.s) or it could be 22 55 10 110 ( non primes)

St. 1 and St. 2 -- HCF * LCM= P* 110 ( standard formula)
Therefore- 11*110= P* 110
Therefore P is 11 ( prime no.) . C is the right answer

Sent from my XT1562 using GMAT Club Forum mobile app

exactly what i had in mind

but LCM is least common multiple and not least common factor

i think there is a typing error in the question
Director
Joined: 20 Sep 2016
Posts: 634
Location: India
Concentration: Strategy, Operations
GPA: 3.95
WE: Operations (Real Estate)
If p is a positive integer, is p prime?  [#permalink]

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20 Mar 2018, 00:09
1
Hatakekakashi wrote:
rishabhmishra wrote:
If p is a positive integer, is p prime?
1. The highest common factor of P and 110 is 11.
2. The least common factor of P and 110 is 110

IMO C

St. 1 not sufficient - HCF is 11 which means that there has to be a 11 in P so P could be 11 and the answer would be yes. But if P is 143 ( 11*13) the HCF is still 11 but here P is not a prime no.

St. 2 Not sufficient. LCM is 110. And the other number is 110 therefore we can conclude that either P is 110 or less than 110. Now LCM = 110= ( 11*5*2) . another number 110= 11*5*2. Now P could be either 11 or 2 or 5 or 55 or 22 or 110. As for LCM we only choose the highest power of prime no.s P cannot have more than 1 ( 11 5 2). There P could be just 11 or 5 or 2 ( prime no.s) or it could be 22 55 10 110 ( non primes)

St. 1 and St. 2 -- HCF * LCM= P* 110 ( standard formula)
Therefore- 11*110= P* 110
Therefore P is 11 ( prime no.) . C is the right answer

Sent from my XT1562 using GMAT Club Forum mobile app

exactly what i had in mind

but LCM is least common multiple and not least common factor

i think there is a typing error in the question

The question says least common multiple!

Sent from my XT1562 using GMAT Club Forum mobile app

I'm a moderator I've edited the question
Manager
Joined: 23 Sep 2016
Posts: 233
Re: If p is a positive integer, is p prime?  [#permalink]

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20 Mar 2018, 00:25
Hatakekakashi wrote:
rishabhmishra wrote:
If p is a positive integer, is p prime?
1. The highest common factor of P and 110 is 11.
2. The least common factor of P and 110 is 110

is the question correct?

acc to B

if 110 is the least common factor

p and 110 are multiples of 110
so p can never b prime

I think you lost in question its least common factor question is absolutely correct....
Current Student
Joined: 07 Jan 2016
Posts: 1088
Location: India
GMAT 1: 710 Q49 V36
Re: If p is a positive integer, is p prime?  [#permalink]

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20 Mar 2018, 00:49
1
rishabhmishra wrote:
Hatakekakashi wrote:
rishabhmishra wrote:
If p is a positive integer, is p prime?
1. The highest common factor of P and 110 is 11.
2. The least common factor of P and 110 is 110

is the question correct?

acc to B

if 110 is the least common factor

p and 110 are multiples of 110
so p can never b prime

I think you lost in question its least common factor question is absolutely correct....

I've edited the question

Posted from my mobile device
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Re: If p is a positive integer, is p prime?  [#permalink]

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02 May 2019, 03:28
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Re: If p is a positive integer, is p prime?   [#permalink] 02 May 2019, 03:28
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