OG-12 PS#159

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itaytay: Newbie | Next Rank: 10 Posts; Posts: 1; Joined: Thu Feb 16, 2012 1:08 pm

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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Source: Beat The GMAT — Problem Solving | Thu Feb 23, 2012 8:17 am

LalaB: Master | Next Rank: 500 Posts; Posts: 425; Joined: Wed Dec 08, 2010 9:00 amFollowed by: 7 members; Thanked: 56 times; GMAT Score:690

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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pemdas: Legendary Member; Posts: 1084; Joined: Fri Apr 15, 2011 2:33 pmFollowed by: 21 members; Thanked: 158 times

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?

Success doesn't come overnight!

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LalaB: Master | Next Rank: 500 Posts; Posts: 425; Joined: Wed Dec 08, 2010 9:00 amFollowed by: 7 members; Thanked: 56 times; GMAT Score:690

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

Happy are those who dream dreams and are ready to pay the price to make them come true.(c)

In order to succeed, your desire for success should be greater than your fear of failure.(c)

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