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If P & Q are positive integers , what is the value of Q [#permalink]
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17 Jun 2007, 02:56
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If P & Q are positive integers , what is the value of Q ?
1. S is the product of two prime numbers greater than 10
2. S=P. Q3 ( Read as Q cube)
I know the answer but I am not convinced with the explaination.Can anybody of you please help.



SVP
Joined: 01 May 2006
Posts: 1796

(C) for me
We have:
p > 0 and q > 0
q=?
From 1
S = i * j where i > 10 and j > 10 and i, j are primes.
No relationship with P or Q....
INSUFF.
From 2
S = p*q^3
S could be anything and so is q...
INSUFF.
Both 1 and 2
p*q^3 = i*j
Implies that, as i & j are primes:
o p = i*j
o q^3 = 1 <=> q = 1
SUFF.



Manager
Joined: 17 May 2007
Posts: 170

Insufficient to answer the question..
Answer E



Director
Joined: 14 Jan 2007
Posts: 774

I agree with Fig.
Q should be 1 to satisfy the equation for all primes > 10.



Director
Joined: 13 Mar 2007
Posts: 543
Schools: MIT Sloan

i dont get the expln for C.
can someone pls explain ?



SVP
Joined: 01 May 2006
Posts: 1796

grad_mba wrote: i dont get the expln for C.
can someone pls explain ?
S is composed of 2 prime integers.... q^3 cannot give a prime integer (ex 11^3, 13^3 are not prime integers), so it must be equal to 1 to not interfer and to make it possible for S to be a multiple of 2 primes integers, provided by p here.



Director
Joined: 13 Mar 2007
Posts: 543
Schools: MIT Sloan

Thx Fig !
appreciate ur enthu in the forum evn after ur long done with ur GMAT !



SVP
Joined: 01 May 2006
Posts: 1796

grad_mba wrote: Thx Fig ! appreciate ur enthu in the forum evn after ur long done with ur GMAT !
U are welcome ... Have u planned to pass the GMAT soon?



Director
Joined: 13 Mar 2007
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Schools: MIT Sloan

Fig wrote: grad_mba wrote: Thx Fig ! appreciate ur enthu in the forum evn after ur long done with ur GMAT ! U are welcome ... Have u planned to pass the GMAT soon?
yes yes .. gives me shivers though !



Senior Manager
Joined: 03 Jun 2007
Posts: 376

This is abad question though. When combining the 2 statements we need to assume both are true. So by stmt 1 we are told that S is a product of 2 prime ints > 10. Using stmt2, q^3 cannot exist at all



Senior Manager
Joined: 19 Feb 2007
Posts: 325

dahcrap wrote: This is abad question though. When combining the 2 statements we need to assume both are true. So by stmt 1 we are told that S is a product of 2 prime ints > 10. Using stmt2, q^3 cannot exist at all
It can if q=1.
eg: S = 11 * 13
also S = (11* 13) * 1^3
S = P * Q^3
Hope this explains.



Director
Joined: 26 Feb 2006
Posts: 899

Fig wrote: (C) for me We have: p > 0 and q > 0 q=? From 1S = i * j where i > 10 and j > 10 and i, j are primes. No relationship with P or Q.... INSUFF. From 2S = p*q^3 S could be anything and so is q... INSUFF. Both 1 and 2p*q^3 = i*j Implies that, as i & j are primes: o p = i*j o q^3 = 1 <=> q = 1 SUFF. amitsamel wrote: If P & Q are positive integers, what is the value of Q ?
1. S is the product of two prime numbers greater than 10 2. S = P . Q^3
I know the answer but I am not convinced with the explaination. Can anybody of you please help.
C. agree with Fig.
if P and Q were positive numbers, the answer would be E. but P and Q are integers, it makes sense Q is 1 and C is the answer.
I too was heading for E but realized the mistake immidiately.



Senior Manager
Joined: 04 Jun 2007
Posts: 366

I still don't see how it's C?
ST. 1 says S is the product of two prime numbers which are both >10
ST. 2 gives us S= P*Q^3
which means P is a prime>10
and Q^3 is a prime>10
hence Q^3 needs to be a perfect cube + a prime> 10
perfect cubes >10 are 27, 64, 125, none of which are primes
there is no perfect cube which is also a prime> 10
how can we take Q to be equal to 1, that would make Q^3= 1 and 1<10
the answer has to be E.



CEO
Joined: 29 Mar 2007
Posts: 2560

Fig wrote: grad_mba wrote: i dont get the expln for C.
can someone pls explain ? S is composed of 2 prime integers.... q^3 cannot give a prime integer (ex 11^3, 13^3 are not prime integers), so it must be equal to 1 to not interfer and to make it possible for S to be a multiple of 2 primes integers, provided by p here.
Ah ok now I see. I thought S1 was sayin that S is the product of 2 primes that are both greater than 10.
Was like how can this be C?



Director
Joined: 08 Jun 2007
Posts: 573

Re: Tricky DS [#permalink]
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10 Sep 2007, 20:57
Well it got me nuts first. But finally managed C.
Fig gr8 explanation.



Senior Manager
Joined: 04 Jun 2007
Posts: 366

GMATBLACKBELT wrote: Fig wrote: grad_mba wrote: i dont get the expln for C.
can someone pls explain ? S is composed of 2 prime integers.... q^3 cannot give a prime integer (ex 11^3, 13^3 are not prime integers), so it must be equal to 1 to not interfer and to make it possible for S to be a multiple of 2 primes integers, provided by p here. Ah ok now I see. I thought S1 was sayin that S is the product of 2 primes that are both greater than 10. Was like how can this be C?
exactly, I am not sure why everyone is agreeing that Q is 1 when ST. 1& 2 implies clearly that Q^3 must be a prime> 10.
1 is not a prime and it is not greater than 10.



Senior Manager
Joined: 27 Aug 2007
Posts: 253

Totally agree with Fig, it is C
since prime number cannot be equal to the number n^3 because it says it is prime...
however, Sometimes I dont understand what is saying the question, can smn give me advice how to cope with it???










