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The sum of n consecutive positive integers is 45. What is the value of n? (1) n is even (2) n < 9

For me its C. Any thoughts guys?

The sum of n consecutive positive integers is 45. What is the value of n?

(1) n is even --> n can be 2: 22+23=45. But it also can be 6 --> x+(x+1)+(x+2)+(x+3)+(x+4)+(x+5)=45 --> x=5. At least two values of n are possible. Not sufficient.

(2) n<9 --> the above example is also valid for this statement, hence not sufficient.

(1)+(2) Still at least two values of n are possible. Not sufficient.

Re: The sum of n consecutive positive integers is 45. What is [#permalink]
24 Sep 2012, 03:12

Expert's post

venmic wrote:

Bunuel

my question is hovv do you knovv vvhere to stop there could have been an 8 too

When a DS question asks about the value of some variable, then the statement(s) is sufficient ONLY if you can get the single numerical value of this variable.

Now, when we consider the two statements together we have that n can be 2 or 6, so we don't have single numerical value of n, which means that the answer is E. We don't need to find whether n can be some other number, since two values are enough to tell that the statements taken together are not sufficient.

Re: The sum of n consecutive positive integers is 45. What is [#permalink]
06 Oct 2012, 04:52

Bunuel wrote:

venmic wrote:

Bunuel

my question is hovv do you knovv vvhere to stop there could have been an 8 too

When a DS question asks about the value of some variable, then the statement(s) is sufficient ONLY if you can get the single numerical value of this variable.

Now, when we consider the two statements together we have that n can be 2 or 6, so we don't have single numerical value of n, which means that the answer is E. We don't need to find whether n can be some other number, since two values are enough to tell that the statements taken together are not sufficient.

Hope it's clear.

Hey Bunuel,

How about this approach-

The sum of n consecutive numbers is n (n+1)/2=45 Therefore- n(n+1)=90 ...> n^2+n-90=0 ....> n-9=0 or n=-10

so both 1 and 2 are sufficient to answer. So the answer must be D right?? _________________

I've failed over and over and over again in my life and that is why I succeed--Michael Jordan Kudos drives a person to better himself every single time. So Pls give it generously Wont give up till i hit a 700+

Re: The sum of n consecutive positive integers is 45. What is [#permalink]
06 Oct 2012, 07:09

2

This post received KUDOS

rajathpanta wrote:

Bunuel wrote:

venmic wrote:

Bunuel

my question is hovv do you knovv vvhere to stop there could have been an 8 too

When a DS question asks about the value of some variable, then the statement(s) is sufficient ONLY if you can get the single numerical value of this variable.

Now, when we consider the two statements together we have that n can be 2 or 6, so we don't have single numerical value of n, which means that the answer is E. We don't need to find whether n can be some other number, since two values are enough to tell that the statements taken together are not sufficient.

Hope it's clear.

Hey Bunuel,

How about this approach-

The sum of n consecutive numbers is n (n+1)/2=45 Therefore- n(n+1)=90 ...> n^2+n-90=0 ....> n-9=0 or n=-10

so both 1 and 2 are sufficient to answer. So the answer must be D right??

The sum of n consecutive numbers is n (n+1)/2=45 NO The sum of the first n consecutive positive integers 1, 2, 3,..., n is n(n + 1)/2. Nowhere is stated that we have some number of the first positive integers. _________________

PhD in Applied Mathematics Love GMAT Quant questions and running.

Re: The sum of n consecutive positive integers is 45. What is [#permalink]
06 Oct 2012, 08:20

Thanks EVa... got it _________________

I've failed over and over and over again in my life and that is why I succeed--Michael Jordan Kudos drives a person to better himself every single time. So Pls give it generously Wont give up till i hit a 700+

The sum of n consecutive positive integers is 45 [#permalink]
18 May 2013, 22:50

The sum of n consecutive positive integers is 45. What is the value of n?

(1) n is even

(2) n < 9

Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient. Both statements TOGETHER are sufficient, but NEITHER one ALONE is sufficient. EACH statement ALONE is sufficient. Statements (1) and (2) TOGETHER are NOT sufficient.

Hi Everyone this problem is from Manhattan Practise test 4. This problem looked very simple to me but I am stuck with it. Despite looking at the explanation which is long and hard to understand, I couldn't understand what so ever. However while I was giving exam I thought that there is a formula for the sum of n consecutive positive integers which is n(n+1)/2 and this problem could be solved easily. But that doesn't apply to this problem. Can someone please help me with this.

Re: The sum of n consecutive positive integers is 45 [#permalink]
18 May 2013, 23:34

Expert's post

tk1tez7777 wrote:

The sum of n consecutive positive integers is 45. What is the value of n?

(1) n is even

(2) n < 9

Let the first term be a, which is a positive integer. Thus, given that\frac{n}{2}[2a+(n-1)] = 45

From F.S 1, we know that n=even, thus 2a+(n-1) = even+odd=odd.

Thus,\frac{n}{2}*odd =\frac{10}{2}*9. It could also be =\frac{6}{2}*15 Insufficient.

From F.S 2, we know that n<9. Thus, \frac{90}{n} must be an integer.We have n=1 or 2 or 3 or 5 or 6.Insufficient. Taking both together , we have n = 2 or 6. Insufficient. E. _________________

Re: The sum of n consecutive positive integers is 45 [#permalink]
19 May 2013, 02:18

Expert's post

tk1tez7777 wrote:

The sum of n consecutive positive integers is 45. What is the value of n?

(1) n is even

(2) n < 9

Statement (1) ALONE is sufficient, but statement (2) alone is not sufficient. Statement (2) ALONE is sufficient, but statement (1) alone is not sufficient. Both statements TOGETHER are sufficient, but NEITHER one ALONE is sufficient. EACH statement ALONE is sufficient. Statements (1) and (2) TOGETHER are NOT sufficient.

Hi Everyone this problem is from Manhattan Practise test 4. This problem looked very simple to me but I am stuck with it. Despite looking at the explanation which is long and hard to understand, I couldn't understand what so ever. However while I was giving exam I thought that there is a formula for the sum of n consecutive positive integers which is n(n+1)/2 and this problem could be solved easily. But that doesn't apply to this problem. Can someone please help me with this.

OA is E.

Thanks In advance.

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