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PS-how many prime numbers are less than 100?

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PS-how many prime numbers are less than 100?

by nitya34 » Thu Jul 23, 2009 8:38 am
how many prime numbers are less than 100?
options are
22,23,24,25,26
any short cut here?
OA is 25
Last edited by nitya34 on Fri Jul 24, 2009 12:02 am, edited 1 time in total.
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Re: PS-how many prime numbers are less than 100?

by Stuart@KaplanGMAT » Thu Jul 23, 2009 9:18 am
nitya34 wrote:how many prime numbers are less than 100?

any short cut here?
OA is 25
This is not a real GMAT question.

Mathematicians have devoted their entire careers to finding ways to list prime numbers - there is no simple shortcut. The only possible way a GMAT test taker could be expected to answer the question is to actually list all the numbers from 1 to 100 and count the primes.

Where is this question from? What were the answer choices? You should include both of these pieces of info in every post you make on this forum.
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by PussInBoots » Fri Jul 24, 2009 10:01 pm
It cannot be GMAT question. The only way to do it is to go through every odd number and check if it's prime or not
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by prindaroy » Fri Jul 24, 2009 11:29 pm
Certainly not a GMAT question. But to answer your question, the number of primes less than can be approximated to n/ln(n-1) = 100/ln(100-1). There have also been several functions to determine number of primes.
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