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Hard time with a DS question. Please help

Expert replies
by shoot4greatness » Thu Nov 18, 2010 12:52 pm
The question states:

How many prime numbers are less than integer K?

1)18<K<27
2)23<K<30

The firsr part, I do know that it's unclear because we don't know 19 AND/OR 23 is less than K. A and D are out.
The secon part, all primes upto 23 are less than K. But how about 29? Do I assume K itself is not 29 (the question states K is an interger but did not say if it is also a prime number)?

The answer is B. But as I stated prior, the second part sounds pretty tricky to me. Please help. Thanks in advance.
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Source: — Data Sufficiency |

by Rahul@gurome » Thu Nov 18, 2010 1:30 pm
shoot4greatness wrote:How many prime numbers are less than integer K?

1)18<K<27
2)23<K<30
The question asks for number of prime numbers which are less than K!

Statement 1: 18 < K < 27.
There are two primes (19 and 23) in between 18 and 27. Now K may be greater than 23 or less than 19 or in between.

Not sufficient.

Statement 2: 23 < K < 30.
there is only one prime (29) in between 23 and 30. Now K is either less than or equal to 29. In any case number of prime numbers less than K will be same. They are 2, 3, 5, 7, 11, 13, 17, 19 and 23!

Sufficient!

The correct answer is B.
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by shoot4greatness » Thu Nov 18, 2010 2:09 pm
OK I get it now whether K is 29 or not the question is asking primes less than K. Even if K is 29, we looking at primes less than 29. Got it. Thanks.
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