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Sorry for posting this, it may sound silly to someone, but I have problem understanding the question:

How many integers n are there such that r < n < s? (1) s - r = 5 (2) r and s are not integers.

My solution: For (1), whether r and s are integer or not, there can be so many "groups" of 4 or 5 n that fit the conditions.

So (1) not enough and (2) not enough, apparently (1) and (2) not enough, according to my "reasoning" above.

So I chose E Please comment, thanks

The question is: how many integers \(n\) satisfy \(r < n < s\), or how many integers are between \(r\) and \(s\), not inclusive?

Note that if \(r\) and \(s\) are integers, for example \(s=5\) and \(r=0\) then there will be 4 integers between them: 1, 2, 3, and 4. But if \(r\) and \(s\) are NOT integers for example \(s=5.5\) and \(r=0.5\) then there will be 5, so one more, integers between them: 1, 2, 3, 4 and 5.

The "number" of n can be multiple of 4 or 5, says 8 or 10, 12, 15, ... can not be determined...

It seems that you misinterpreted the question.

Question ask about the number of integers between r and s, not inclusive.

For example: how many integers are between 10 and 15, not inclusive? Answer: 4, namely 11, 12, 13, and 14. Or: how many integers are between 5.3 and 10.3? Answer: 5, namely 5, 6, 7, 8, 9 and 10.

So taken together statements are sufficient to answer that there are 5 integers between r and s.

this is one of the trickiest questions I have ever seen so far - in test conditions - time and pressure, I am not going to consider C as an option EVER, since there are 5 values for n ... but it is actually that 5 is what the question is looking for ... tough one

Re: How many integers n are there such that r < n< 5 ? [#permalink]
22 Apr 2012, 12:44

1

This post received KUDOS

Expert's post

1

This post was BOOKMARKED

How many integers n are there such that r < n< s ?

The question asks: how many integers \(n\) satisfy \(r < n < s\), or how many integers are between \(r\) and \(s\), not inclusive?

Notice that if \(r\) and \(s\) are integers, for example \(s=5\) and \(r=0\) then there will be 4 integers between them: 1, 2, 3, and 4. But if \(r\) and \(s\) are NOT integers for example \(s=5.5\) and \(r=0.5\) then there will be 5, so one more, integers between them: 1, 2, 3, 4 and 5.

(1) s - r = 5. Not sufficient. (2) r and s are not integers. Not sufficient.

(1)+(2) According to above reasoning since r and s are not integers then there are 5 integers between them (case 2). Sufficient.

Re: How many integers n are there such that r < n< s ? [#permalink]
22 Apr 2012, 13:00

Thanks for putting this together. I received a 29 on my last math section of the GMAT. Any suggestions for improvement since I take it again on May 31st? Why did you choose that picture? I like it and have not seen anything similar to it.

Re: How many integers n are there such that r < n< 5 ? [#permalink]
22 Apr 2012, 13:09

Expert's post

Bunuel wrote:

How many integers n are there such that r < n< s ?

The question asks: how many integers \(n\) satisfy \(r < n < s\), or how many integers are between \(r\) and \(s\), not inclusive?

Notice that if \(r\) and \(s\) are integers, for example \(s=5\) and \(r=0\) then there will be 4 integers between them: 1, 2, 3, and 4. But if \(r\) and \(s\) are NOT integers for example \(s=5.5\) and \(r=0.5\) then there will be 5, so one more, integers between them: 1, 2, 3, 4 and 5.

(1) s - r = 5. Not sufficient. (2) r and s are not integers. Not sufficient.

(1)+(2) According to above reasoning since r and s are not integers then there are 5 integers between them (case 2). Sufficient.

Answer: C.

Hope it's clear.

can you please eleborate the concept behind this ?? indeed is true but I didn't notice this before.

Re: How many integers n are there such that r < n< 5 ? [#permalink]
22 Apr 2012, 13:15

Expert's post

carcass wrote:

Bunuel wrote:

How many integers n are there such that r < n< s ?

The question asks: how many integers \(n\) satisfy \(r < n < s\), or how many integers are between \(r\) and \(s\), not inclusive?

Notice that if \(r\) and \(s\) are integers, for example \(s=5\) and \(r=0\) then there will be 4 integers between them: 1, 2, 3, and 4. But if \(r\) and \(s\) are NOT integers for example \(s=5.5\) and \(r=0.5\) then there will be 5, so one more, integers between them: 1, 2, 3, 4 and 5.

(1) s - r = 5. Not sufficient. (2) r and s are not integers. Not sufficient.

(1)+(2) According to above reasoning since r and s are not integers then there are 5 integers between them (case 2). Sufficient.

Answer: C.

Hope it's clear.

can you please eleborate the concept behind this ?? indeed is true but I didn't notice this before.

Thanks

There isn't some special concept behind it. It's just common sense based on observation. _________________

Re: How many integers n are there such that r < n < s? [#permalink]
30 Dec 2012, 18:50

hmm... I chose E with the reasoning that the question does not mention that the integers are consecutive. There could be duplicate integers between r and s such that r=0 and s=5 and values of n to be 1, 1, 2, 3, 4, 4.

Re: How many integers n are there such that r < n < s? [#permalink]
31 Dec 2012, 02:22

Expert's post

4sguy wrote:

hmm... I chose E with the reasoning that the question does not mention that the integers are consecutive. There could be duplicate integers between r and s such that r=0 and s=5 and values of n to be 1, 1, 2, 3, 4, 4.

Re: How many integers n are there such that r < n < s? [#permalink]
18 Jun 2013, 19:35

I had and still continue to have trouble interpreting this question.

how many integers n are there such that r<n<s r and s are 0 or 5 -> n can be 1,2,3,4 r and s are 110 or 115-> n can be another set of 4 no.s

i thought n can have any number of infinite values for r-s=5 or for r and s are not integers.....can some one pls make it clear...

i understand some of the explanations are towards n=no. of integers between two given values, but question ask how many integers n are there that meet the criteria...

Re: How many integers n are there such that r < n < s? [#permalink]
19 Jun 2013, 01:36

1

This post received KUDOS

Expert's post

nanz236 wrote:

I had and still continue to have trouble interpreting this question.

how many integers n are there such that r<n<s r and s are 0 or 5 -> n can be 1,2,3,4 r and s are 110 or 115-> n can be another set of 4 no.s

i thought n can have any number of infinite values for r-s=5 or for r and s are not integers.....can some one pls make it clear...

i understand some of the explanations are towards n=no. of integers between two given values, but question ask how many integers n are there that meet the criteria...

How many integers n are there such that 0 < n < 5? Answer: 4. How many integers n are there such that 110 < n < 115? Answer: 4.

Re: How many integers n are there such that r < n< s ? [#permalink]
18 May 2014, 09:46

1

This post received KUDOS

if we knew about s and r (integers or not integers) our task would be simplified to st(1) Suff. Since we know nothing about s and r, there could be always four integers (case when s and r are integers) or five integers (when s or r is not integer)

st(2) helps with assigning type for our numbers (s and r), but we know nothing about values

combined st(1&2) supports our previously inquired data, i.e. s and r are not integers, hence the number of integers in the given interval will always be 5.

Re: How many integers n are there such that r < n < s? [#permalink]
05 Dec 2014, 20:35

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