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OG-12 PS#159

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OG-12 PS#159

by itaytay » Thu Feb 23, 2012 8:17 am
Hello everyone.

The question asks how many prime numbers between 1 and 100 are factos of 7,150.

Prime factoring of 7,150 results in 2X5X5X11X13. According to the OG, the answer is therefore "4".

However, We were not asked how many DISTINCT prime numbers are factors of 7,150, but how many prime numbers are there. Shouldn't the answer therefore be 5?
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by LalaB » Thu Feb 23, 2012 10:19 am
please pay attention to this fact from the q.stem -how many prime numbers between 1 and 100
it means that u have 2 3 5 7 11 etc
so,for sure, u do not have two 5 between 1 and 100 ;)
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by pemdas » Thu Feb 23, 2012 10:27 am
IOM the question asks 'how many prime numbers are factors' and not 'how many prime factors'. For example if you say 5 is a prime number, i.e. one number and it's a factor of 7,150 then you CANNOT say 5 is two prime numbers which are factors of 7,150.

Though I agree, this question's wording could be a bit rephrased. If this were GMAT question, it would be an experimental one I guess.
itaytay wrote:Hello everyone.

The question asks how many prime numbers between 1 and 100 are factos of 7,150.

Prime factoring of 7,150 results in 2X5X5X11X13. According to the OG, the answer is therefore "4".

However, We were not asked how many DISTINCT prime numbers are factors of 7,150, but how many prime numbers are there. Shouldn't the answer therefore be 5?
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by LalaB » Thu Feb 23, 2012 10:34 am
the q says u have prime numbers between 1 and 100 ( 2 3 5 7 11 etc )
and then asks u -
how many of these numbers are factors of 7150.


7150=2*5*5*11*13

if u dont have the 1st phrase about 1 and 100, then u will answer- there are 5 numbers

but since u are asked how many of these 2 3 5 7 11 etc are factors of 7150, ur answer should be 4, since u dont have two 5's (or any other number) on a number line
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