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Re: prime factors of n [#permalink]
04 Sep 2008, 02:42
Answer is B.
From stmt 1, N is a multiple of 5 in such that N is obtained by multiplying 5 with another prime number.
Thus, N can be 10, 15, 25, 35, 55...... i.e. N can have 1 prime factor (e.g. 25) or 2 (e.g. 10, 15,...)....hence not sufficient.
From stmt2, 3 is already a prime factor. Hence, in order for 3N^2 to have two different prime factor, N^2 has to be a perfect square of a prime number. This implies that N itself is a prime number and hence will have only one prime factor. Hence, sufficient.
Re: prime factors of n [#permalink]
04 Sep 2008, 04:46
arjtryarjtry wrote:
How many prime factors does positive integer N have? (1) N/5 is a prime number. (2) 3N^2 has two different prime number.
D.
If N/5 is a prime number, then N=5*x where x is a prime number. So N has only two prime factors.
if 3*N^2 has two different prime factors, then 3 is one of them and N is the other. In this case, N has to be a prime number and hence will have only one prime factor
Re: prime factors of n [#permalink]
04 Sep 2008, 04:52
IMO C.
1) N = 5a, where a is any prime number. N can have one or two prime factors. Not sufficient 2) 3N^2 has two different prime factors. Not sufficient, because N can have one prime factor, or two prime factors (f.ex. N=21=3*7).
Combine both - N can be 25 or 15, i.e. two prime factors. _________________
Re: prime factors of n [#permalink]
04 Sep 2008, 07:03
arjtryarjtry wrote:
How many prime factors does positive integer N have? (1) N/5 is a prime number. (2) 3N^2 has two different prime number.
(1) N/5 is a prime number. N= 5* x it doesn't matter.. whether x=5 or 3 .. N has two prime factors. N=5*5 ( two prime factors.... though not two different prime factors.)
Question is How many prime factors does positive integer N have? Ans 2
(2) 3N^2 has two different prime number.[/ N must be prime number. sufficient.
D.
If question Says How many different prime factors does positive integer N have? then Ans would be C. _________________
Your attitude determines your altitude Smiling wins more friends than frowning
Re: prime factors of n [#permalink]
04 Sep 2008, 07:24
x2suresh wrote:
arjtryarjtry wrote:
How many prime factors does positive integer N have? (1) N/5 is a prime number. (2) 3N^2 has two different prime number.
(1) N/5 is a prime number. N= 5* x it doesn't matter.. whether x=5 or 3 .. N has two prime factors. N=5*5 ( two prime factors.... though not two different prime factors.)
Question is How many prime factors does positive integer N have? Ans 2
(2) 3N^2 has two different prime number.[/ N must be prime number. sufficient.
D.
If question Says How many different prime factors does positive integer N have? then Ans would be C.
another good catch gosh... hopefully the real test will leave no room for ambiguity .
Re: prime factors of n [#permalink]
04 Sep 2008, 22:50
Nerdboy wrote:
IMO C.
1) N = 5a, where a is any prime number. N can have one or two prime factors. Not sufficient 2) 3N^2 has two different prime factors. Not sufficient, because N can have one prime factor, or two prime factors (f.ex. N=21=3*7).
Combine both - N can be 25 or 15, i.e. two prime factors.
Guys, I messed up completely. If N can be 25 or 15, then answer is E - assuming we are looking for different prime factors. If we are looking for number of prime factors, not necessarily different, then it should be A. OA? _________________
Re: prime factors of n [#permalink]
04 Sep 2008, 23:26
While I await the OA....I have one question here.
If I take the number 25, do I say, it has two prime factors? does it not have only one prime factor and that is 5? 25 can be divided by 5 and 5 is a prime factor. why do I have to count 5 again?
gmatclubot
Re: prime factors of n
[#permalink]
04 Sep 2008, 23:26