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Need clarification on finding Prime Factors

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Intern
Joined: 14 Apr 2015
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GMAT Date: 06-14-2015
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Need clarification on finding Prime Factors  [#permalink]

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02 May 2015, 14:27
1
Quant is not my strength, so this question may seem a bit silly, but when a question asks "how many prime factors does X have?" In general, does it mean unique prime factors?

For example the prime factors of 48, {(2^4), 3}
If a question asks, how many prime factors does 48 have? Would you answer two, or five? Will a question specifically ask for Unique Prime Factors if that's what it is looking for?
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Re: Need clarification on finding Prime Factors  [#permalink]

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02 May 2015, 15:36
3
meshackb wrote:
Quant is not my strength, so this question may seem a bit silly, but when a question asks "how many prime factors does X have?" In general, does it mean unique prime factors?

For example the prime factors of 48, {(2^4), 3}
If a question asks, how many prime factors does 48 have? Would you answer two, or five? Will a question specifically ask for Unique Prime Factors if that's what it is looking for?

Hello meshackb
So 48 has two prime factors: 2 and 3
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Re: Need clarification on finding Prime Factors  [#permalink]

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12 May 2015, 22:20
Harley1980 wrote:
meshackb wrote:
Quant is not my strength, so this question may seem a bit silly, but when a question asks "how many prime factors does X have?" In general, does it mean unique prime factors?

For example the prime factors of 48, {(2^4), 3}
If a question asks, how many prime factors does 48 have? Would you answer two, or five? Will a question specifically ask for Unique Prime Factors if that's what it is looking for?

Hello meshackb
So 48 has two prime factors: 2 and 3

Hey Harley1980, can you provide an official example that deals with prime factors, and the official answer only means unique (without stating "unique" or "different" somewhere in the problem)? I was taking a look through MGMAT's Number Properties book (5th ed) and when they talk about counting prime factors they state that the total number of prime factors of 252 is 5 (2,2,3,3,7) (top of pg 96). On the previous page they talk about the different ways that factor questions can be asked, and they explicitly state "different prime factors" or "unique prime factors" when the answer should only be 2,3,7 - for the previous example. There are also some previous examples in the book when they mention prime factors they explicitly state all of the multiplicities.

I'm coming from an academic math background, so my understanding of prime factorization stems from that.
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Re: Need clarification on finding Prime Factors  [#permalink]

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12 May 2015, 23:43
1
wakk0 wrote:
Harley1980 wrote:
meshackb wrote:
Quant is not my strength, so this question may seem a bit silly, but when a question asks "how many prime factors does X have?" In general, does it mean unique prime factors?

For example the prime factors of 48, {(2^4), 3}
If a question asks, how many prime factors does 48 have? Would you answer two, or five? Will a question specifically ask for Unique Prime Factors if that's what it is looking for?

Hello meshackb
So 48 has two prime factors: 2 and 3

Hey Harley1980, can you provide an official example that deals with prime factors, and the official answer only means unique (without stating "unique" or "different" somewhere in the problem)? I was taking a look through MGMAT's Number Properties book (5th ed) and when they talk about counting prime factors they state that the total number of prime factors of 252 is 5 (2,2,3,3,7) (top of pg 96). On the previous page they talk about the different ways that factor questions can be asked, and they explicitly state "different prime factors" or "unique prime factors" when the answer should only be 2,3,7 - for the previous example. There are also some previous examples in the book when they mention prime factors they explicitly state all of the multiplicities.

I'm coming from an academic math background, so my understanding of prime factorization stems from that.

Hello wakk0.

Here is example
the-positive-integer-k-has-exactly-two-positive-prime-factor-60634.html
in which task says that number k has exactly two primes. And after we solved task we can see that k = 63 so k = 3 * 3 * 7 and has 3 prime factors with repetions and 2 prime factors without repetions. So we can infer that GMAC count primes without repetions.

But you are absolutely right: this is really uncommon case for official tasks. Usually GMAC questions avoid any ambiguity and clearly specify what we need to seek:

"different prime factors":
how-many-different-prime-numbers-are-factors-of-the-positive-102487.html
if-n-is-the-product-of-the-integers-from-1-to-8-inclusive-50953.html

Or if they want include repetions of primes they mention it as "prime including repetions":
the-prime-sum-of-an-integer-n-greater-than-1-is-the-sum-of-167088.html

and Manhattan example of task in with we should find primes with repetitions "prime factors, not necessarily distinct":
for-any-integer-k-1-the-term-length-of-an-integer-108124.html
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Re: Need clarification on finding Prime Factors  [#permalink]

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29 Jan 2018, 00:05
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Re: Need clarification on finding Prime Factors   [#permalink] 29 Jan 2018, 00:05
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