If the average (arithmetic mean) of n consecutive odd : GMAT Data Sufficiency (DS)
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# If the average (arithmetic mean) of n consecutive odd

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If the average (arithmetic mean) of n consecutive odd [#permalink]

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09 Dec 2010, 14:43
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If the average (arithmetic mean) of n consecutive odd integers is 10, what is the least of the integers?

(1) The range of the n integers is 14

(2) The greatest of the n integers is 17"
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Re: Quant Rev v.2, DS # 66: Consecutive Integer Problem [#permalink]

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09 Dec 2010, 14:59
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tonebeeze wrote:
Hello All,

I got this problem correct. I just would like to see a technical explanation of how to arrive at both occasions of sufficiency.

Thanks!

"If the average (arithmetic mean) of n consecutive odd integers is 10, what is the least of the integers?

(1) The range of the n integers is 14

(2) The greatest of the n integers is 17"

Odd consecutive integers is an evenly spaced set. For any evenly spaced set the mean equals to the average of the first and the last terms, so in our case $$mean=10=\frac{x_1+x_{n}}{2}$$ --> $$x_1+x_{n}=20$$. Question: $$x_1=?$$

(1) The range of the n integers is 14 --> the range of a set is the difference between the largest and smallest elements of a set, so $$x_{n}-x_1=14$$ --> solving for $$x_1$$ --> $$x_1=3$$. Sufficient.

(2) The greatest of the n integers is 17 --> $$x_n=17$$ --> $$x_1+17=20$$ --> $$x_1=3$$. Sufficient.

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Re: Quant Rev v.2, DS # 66: Consecutive Integer Problem [#permalink]

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10 Dec 2010, 06:20
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I say D as well.

Great explanation
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Re: Quant Rev v.2, DS # 66: Consecutive Integer Problem [#permalink]

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12 Dec 2010, 04:24
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tonebeeze wrote:
Hello All,

I got this problem correct. I just would like to see a technical explanation of how to arrive at both occasions of sufficiency.

Thanks!

"If the average (arithmetic mean) of n consecutive odd integers is 10, what is the least of the integers?

(1) The range of the n integers is 14

(2) The greatest of the n integers is 17"

If mean of consecutive odd integers is 10, the sequence of numbers will be something like this:
9, 11 or
7, 9, 11, 13 or
5, 7, 9, 11, 13, 15 or
3, 5, 7, 9, 11, 13, 15, 17 or
1, 3, 5, 7, 9, 11, 13, 15, 17, 19
etc
Every time you add a number to the left, you need to add one to the right to keep the mean 10. The smallest sequence will have 2 numbers 9 and 11, the largest will have infinite numbers.

Stmnt 1: Only one possible sequence: 3, 5, 7, 9, 11, 13, 15, 17 will have range 14. Least of the integers is 3. Sufficient.
Stmnt 2: Only one possible sequence:3, 5, 7, 9, 11, 13, 15, 17
Least of the integers is 3. Sufficient.

Note: You don't actually have to do all this. All such sequences will have distinct number of elements, greatest number, smallest number and range. So each statement alone will be sufficient.
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Get started with Veritas Prep GMAT On Demand for $199 Veritas Prep Reviews SVP Joined: 16 Nov 2010 Posts: 1672 Location: United States (IN) Concentration: Strategy, Technology Followers: 33 Kudos [?]: 514 [1] , given: 36 Re: Quant Rev v.2, DS # 66: Consecutive Integer Problem [#permalink] ### Show Tags 06 Apr 2011, 07:28 1 This post received KUDOS (1) so (a + a + 14)/2 = 10 => 2a = 20 - 14 = 6 => a =3 (2) (a+17)/2 = 10 => a = 3 Answer - D (a+17) _________________ Formula of Life -> Achievement/Potential = k * Happiness (where k is a constant) GMAT Club Premium Membership - big benefits and savings Manager Joined: 15 Apr 2011 Posts: 70 Followers: 0 Kudos [?]: 17 [0], given: 45 Re: If the average (arithmetic mean) of n consecutive odd [#permalink] ### Show Tags 14 Apr 2012, 10:11 Awesome explanation Bunuel! _________________ http://mymbadreamz.blogspot.com Intern Joined: 05 Sep 2012 Posts: 1 Followers: 0 Kudos [?]: 0 [0], given: 8 Re: If the average (arithmetic mean) of n consecutive odd [#permalink] ### Show Tags 29 Sep 2012, 22:27 I think solution D is wrong, what is numbers are : -5, -3, -1, 1, 3,5,7, 9 then range is 14 thus least value in set is : -5 However, if we consider numbers from 3 to 11 then least value is 3. Veritas Prep GMAT Instructor Joined: 16 Oct 2010 Posts: 7132 Location: Pune, India Followers: 2140 Kudos [?]: 13713 [1] , given: 222 Re: If the average (arithmetic mean) of n consecutive odd [#permalink] ### Show Tags 29 Sep 2012, 22:41 1 This post received KUDOS Expert's post bandgmat wrote: I think solution D is wrong, what is numbers are : -5, -3, -1, 1, 3,5,7, 9 then range is 14 thus least value in set is : -5 However, if we consider numbers from 3 to 11 then least value is 3. Yeah, but is the average of these numbers 10? _________________ Karishma Veritas Prep | GMAT Instructor My Blog Get started with Veritas Prep GMAT On Demand for$199

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Re: Quant Rev v.2, DS # 66: Consecutive Integer Problem [#permalink]

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28 Oct 2012, 10:36
Bunuel wrote:
tonebeeze wrote:
Hello All,

I got this problem correct. I just would like to see a technical explanation of how to arrive at both occasions of sufficiency.

Thanks!

"If the average (arithmetic mean) of n consecutive odd integers is 10, what is the least of the integers?

(1) The range of the n integers is 14

(2)The greatest of the n integers is 17"

Odd consecutive integers is an evenly spaced set. For any evenly spaced set the mean equals to the average of the first and the last terms, so in our case $$mean=10=\frac{x_1+x_{n}}{2}$$ --> $$x_1+x_{n}=20$$. Question: $$x_1=?$$

(1) The range of the n integers is 14 --> the range of a set is the difference between the largest and smallest elements of a set, so $$x_{n}-x_1=14$$ --> solving for $$x_1$$ --> $$x_1=3$$. Sufficient.

(2) The greatest of the n integers is 17 --> $$x_n=17$$ --> $$x_1+17=20$$ --> $$x_1=3$$. Sufficient.

Doesn't the highlighted statement actually mean that the highest number in the series is 17??
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Re: Quant Rev v.2, DS # 66: Consecutive Integer Problem [#permalink]

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29 Oct 2012, 01:26
avaneeshvyas wrote:
Bunuel wrote:
tonebeeze wrote:
Hello All,

I got this problem correct. I just would like to see a technical explanation of how to arrive at both occasions of sufficiency.

Thanks!

"If the average (arithmetic mean) of n consecutive odd integers is 10, what is the least of the integers?

(1) The range of the n integers is 14

(2)The greatest of the n integers is 17"

Odd consecutive integers is an evenly spaced set. For any evenly spaced set the mean equals to the average of the first and the last terms, so in our case $$mean=10=\frac{x_1+x_{n}}{2}$$ --> $$x_1+x_{n}=20$$. Question: $$x_1=?$$

(1) The range of the n integers is 14 --> the range of a set is the difference between the largest and smallest elements of a set, so $$x_{n}-x_1=14$$ --> solving for $$x_1$$ --> $$x_1=3$$. Sufficient.

(2) The greatest of the n integers is 17 --> $$x_n=17$$ --> $$x_1+17=20$$ --> $$x_1=3$$. Sufficient.

Doesn't the highlighted statement actually mean that the highest number in the series is 17??

Yes. We generally use the terms greatest/largest.
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Re: If the average (arithmetic mean) of n consecutive odd [#permalink]

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07 Jul 2013, 23:54
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Re: If the average (arithmetic mean) of n consecutive odd [#permalink]

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09 Jul 2013, 06:30
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Let a be the first term. every term in this sequence can be expressed as a+ (i-1) where i ranges from 1 to n. Thus sum of these terms is a*n +1+2+3+..+n-1= an +n(n-1)/2 = 10 n.

(1) We are given that a+n-1 -a =14. We have two eqns for the unkowns (a and n ) and thus (1) is sufficient. No need to actually solve for and and n.

(2) is also sufficient since it is given a+(n-1) =17.

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Re: If the average (arithmetic mean) of n consecutive odd [#permalink]

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09 Jul 2013, 20:57
Or, since this is DS, we can skip the math and use the fact that for a consecutive sequence we only need 2 pieces of information (among mean, smallest number, greatest number, and range) to determine it. So D is correct.
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Re: If the average (arithmetic mean) of n consecutive odd [#permalink]

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Re: If the average (arithmetic mean) of n consecutive odd [#permalink]

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28 Feb 2015, 21:19
As per the question average of n consecutive integers is 10 ;Sum of n consecutive integers =10n
or lets say lowest integer is k then k+ k+2+k+4...+ k+2(n-1) =10n
Simplifying further nk+2(1+2...+n-1)=10n ----> A

lets go with option I

i) The range of n integers is 14

so we know highest integer - lowest integer =14
highest integer =k+2(n-1)
lowest integer =k

Hence we get 2(n-1) =14 or n=8 ,Substituting we get value of k hence I is sufficient

ii) if greatest integer is 17,
then sum would be 17 + 17-2 ...+(17 -(n-1)) = 10n
Simplifying 17n - 2(1+2...+(n-1))=10n or 7n = 2(1+2+...+(n-1))----> B

From A and B we get K=3 ,this sufficient to get all numbers in series Hence II is sufficient
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Re: If the average (arithmetic mean) of n consecutive odd [#permalink]

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09 Oct 2015, 04:43
Below is a very simple logical approach to the problem.

Set={consecutive odd integers} for eg:{3,5,7}---Avg=5(an odd number;this is because number of integers in set= odd)
Avg given=10 (even number)
Thus, obviously the number of terms are even. For eg: {9;11} or {7,9,11,13} Avg:10
Thus; possible entries in set={1,3,5,7,9,11,13,15,17}

1) range=Greatest-least= 14
Check set above ;only 17-3=14 ; thus highest number is 17,lowest 3-- Sufficient

2) Greatest =17
in consecutive integer set greatest+lowest/2= mean
17+Low/2=10
Low= 3 ~~ sufficient.

ANS= D
Hope I was clear.
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Re: If the average (arithmetic mean) of n consecutive odd [#permalink]

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23 Oct 2016, 02:48
Bunuel wrote:
tonebeeze wrote:
Hello All,

I got this problem correct. I just would like to see a technical explanation of how to arrive at both occasions of sufficiency.

Thanks!

"If the average (arithmetic mean) of n consecutive odd integers is 10, what is the least of the integers?

(1) The range of the n integers is 14

(2) The greatest of the n integers is 17"

Odd consecutive integers is an evenly spaced set. For any evenly spaced set the mean equals to the average of the first and the last terms, so in our case $$mean=10=\frac{x_1+x_{n}}{2}$$ --> $$x_1+x_{n}=20$$. Question: $$x_1=?$$

(1) The range of the n integers is 14 --> the range of a set is the difference between the largest and smallest elements of a set, so $$x_{n}-x_1=14$$ --> solving for $$x_1$$ --> $$x_1=3$$. Sufficient.

(2) The greatest of the n integers is 17 --> $$x_n=17$$ --> $$x_1+17=20$$ --> $$x_1=3$$. Sufficient.

Bunuel ,

My question is from the problem statement itself only one solution is possible. [ 3,5,7,9,11,13,15,17]. Are there any chances to encounter such a question on actual exam
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Re: If the average (arithmetic mean) of n consecutive odd [#permalink]

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23 Oct 2016, 05:32
rt1601 wrote:
Bunuel wrote:
tonebeeze wrote:
Hello All,

I got this problem correct. I just would like to see a technical explanation of how to arrive at both occasions of sufficiency.

Thanks!

"If the average (arithmetic mean) of n consecutive odd integers is 10, what is the least of the integers?

(1) The range of the n integers is 14

(2) The greatest of the n integers is 17"

Odd consecutive integers is an evenly spaced set. For any evenly spaced set the mean equals to the average of the first and the last terms, so in our case $$mean=10=\frac{x_1+x_{n}}{2}$$ --> $$x_1+x_{n}=20$$. Question: $$x_1=?$$

(1) The range of the n integers is 14 --> the range of a set is the difference between the largest and smallest elements of a set, so $$x_{n}-x_1=14$$ --> solving for $$x_1$$ --> $$x_1=3$$. Sufficient.

(2) The greatest of the n integers is 17 --> $$x_n=17$$ --> $$x_1+17=20$$ --> $$x_1=3$$. Sufficient.

Bunuel ,

My question is from the problem statement itself only one solution is possible. [ 3,5,7,9,11,13,15,17]. Are there any chances to encounter such a question on actual exam

Unfiniftley many sets are possible:
{9, 11}
{7, 9, 11, 13}
{5, 7, 9, 11, 13, 15}
...
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Re: If the average (arithmetic mean) of n consecutive odd   [#permalink] 23 Oct 2016, 05:32
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