Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

E is a collection of four ODD integers and the greatest [#permalink]

Show Tags

25 Aug 2010, 07:41

5

This post received KUDOS

18

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

85% (hard)

Question Stats:

44% (02:11) correct
56% (04:36) wrong based on 328 sessions

HideShow timer Statistics

E is a collection of four ODD integers and the greatest difference between any two integers in E is 4. The standard deviation of E must be one of how many numbers?

J is a collection of four odd integers whose range is 4. The standard deviation of J must be one of how many numbers?

a 3 b 4 c 5 d 6 e 7

Please explain your thought process on this one. Thanks

This is a good question though I did not like the wording very much. Instead of 'SD of J must be one one how many numbers', 'How many distinct values can SD of J take' is better. Anyway,

First I thought J is a set of four odd integers with range 4 so I said J = {1, x, y, 5} Now x and y can take 3 different values: 1, 3 or 5 Either both x and y are same. This can be done in 3 ways. Or x and y are different. This can be done in 3C2 ways = 3 ways Total x and y can take values in 3 + 3 = 6 ways Let me enumerate them for clarification: {1, 1, 1, 5}, {1, 3, 3, 5}, {1, 5, 5, 5}, {1, 1, 3, 5}, {1, 1, 5, 5}, {1, 3, 5, 5} These are the 6 ways in which you can choose the numbers. Important thing: SD of {1, 1, 1, 5} and {1, 5, 5, 5} is same. Why? SD measures distance from mean. It has nothing to do with the actual value of mean and actual value of numbers. In {1, 1, 1, 5}, mean is 2. Three of the numbers are distance 1 away from mean and one number is distance 3 away from mean. In {1, 5, 5, 5}, mean is 4. Three of the numbers are distance 1 away from mean and one number is distance 3 away from mean.

Similarly, {1, 1, 3, 5} and {1, 3, 5, 5} will have the same SD.

Then, {1, 3, 3, 5} will have a distinct SD and {1, 1, 5, 5} will have a distinct SD. In all, there are 4 different values that SD can take in such a case.

Note: It doesn't matter what the actual numbers are. SD of 1, 3, 5, 7 is the same as SD of 12, 14, 16, 18. For detailed explanation of SD and how to calculate it, check the theory or Stats. _________________

I dont think this is a hard question, expecially if it only asks for odd integers. You do not need to plug in any values and certainly no calculations needed. All you need is a fundamental understanding of what standard deviation means. It is a measure of variation in the set or the distribution of numbers. So without loss of generality if you know the range you can easily enumerate the numbers. Let the 5 dashes below represent the range within which our four integers lie and I will use x's to denote the place of each constituent of the set :

- - - - -

Now, I know the range is 4, so there must be an "x" at the beginning and at the end :

x - - - x

I also know all numbers are odd so the other two numbers can only lie on either the first middle or last place giving me the arrangements :

xx - - - xx x - xx - x xx - x - x xxx - - - x

Note that since standard deviation is a second order measure which measures the distribution of numbers it will be exactly the same for the sets "xx - x - x" and "x - x - xx". So we don't need to enumerate symmetric cases

I dont think this is a hard question, expecially if it only asks for odd integers. You do not need to plug in any values and certainly no calculations needed. All you need is a fundamental understanding of what standard deviation means. It is a measure of variation in the set or the distribution of numbers. So without loss of generality if you know the range you can easily enumerate the numbers. Let the 5 dashes below represent the range within which our four integers lie and I will use x's to denote the place of each constituent of the set :

- - - - -

Now, I know the range is 4, so there must be an "x" at the beginning and at the end :

x - - - x

I also know all numbers are odd so the other two numbers can only lie on either the first middle or last place giving me the arrangements :

xx - - - xx x - xx - x xx - x - x xxx - - - x

Note that since standard deviation is a second order measure which measures the distribution of numbers it will be exactly the same for the sets "xx - x - x" and "x - x - xx". So we don't need to enumerate symmetric cases

Answer is 4

I'd like to clear something for the people who are preparing for GMAT: this might not be a hard question for professional statistician but if such question ever appear on GMAT it'll be considered 750+, so very hard.

Usually GMAT SD questions are fairly straightforward and don't require actual calculation of SD, they are about the general understanding of the concept.

So don't be scared: it's really unlikely you'll see such a question on GMAT and if you will, then you must know that you are doing very well and are probably very close to 51 on quant. _________________

All you need is a fundamental understanding of standard deviation to solve this question, plugging in values is painful and not required. Standard deviation measures how the elements of a set are distributed around the mean, or the "deviation" of the elements in other words. If you have just 4 elements in which the first and last are fixed relative to each other it just boils down to how you can distribute the other two to form different amounts of deviation.

The actual enumeration of this is shown above, but all you you need to note is that the deviation is symmetric cases is just the same :

{1,1,3,5} {1,3,5,5} OR xx - x - x x - x - xx

The deviation is exactly the same, its just the mean which is shifted.

Keeping this in mind there are only 4 possibilities with 4 odd numbers of range 4. _________________

E is a collection of four ODD integers and the greatest difference between any two integers in E is 4. The standard deviation of E must be one of how many numbers? (A) 3 (B) 4 (C) 5 (D) 6 (E) 7

Let the smallest odd integer be 1, thus the largest one will be 5. We can have following 6 types of sets:

CALCULATING STANDARD DEVIATION OF A SET {x1, x2, ... xn}: 1. Find the mean, \(m\), of the values. 2. For each value \(x_i\) calculate its deviation (\(m-x_i\)) from the mean. 3. Calculate the squares of these deviations. 4. Find the mean of the squared deviations. This quantity is the variance. 5. Take the square root of the variance. The quantity is th SD.

Expressed by formula: \(standard \ deviation= \sqrt{variance} = \sqrt{\frac{\sum(m-x_i)^2}{N}}\).

You can see that deviation from the mean for 2 pairs of the set is the same, which means that SD of 1 and 6 will be the same and SD of 2 and 5 also will be the same. So SD of such set can take only 4 values.

as range is 4..we know there is a lowest and there is a highest number Now for the rest 2 numbers:

1) either they are equal to lowest number ... >> 1 SD 2) either they are equal to highest number... >> 1 SD 3) either one is equal to lowest number and one is equal to highest number... >> 1 SD 4) they are same but not equal to lowest or highest number... >> 1 SD

So 4 possibilities (please note that all the numbers can not be distinct..otherwise range will be greater than 4)

J is a collection of four odd integers whose range is 4. The standard deviation of J must be one of how many numbers?

a 3 b 4 c 5 d 6 e 7

Please explain your thought process on this one. Thanks

This is a good question though I did not like the wording very much. Instead of 'SD of J must be one one how many numbers', 'How many distinct values can SD of J take' is better. Anyway,

First I thought J is a set of four odd integers with range 4 so I said J = {1, x, y, 5} Now x and y can take 3 different values: 1, 3 or 5 Either both x and y are same. This can be done in 3 ways. Or x and y are different. This can be done in 3C2 ways = 3 ways Total x and y can take values in 3 + 3 = 6 ways Let me enumerate them for clarification: {1, 1, 1, 5}, {1, 3, 3, 5}, {1, 5, 5, 5}, {1, 1, 3, 5}, {1, 1, 5, 5}, {1, 3, 5, 5} These are the 6 ways in which you can choose the numbers. Important thing: SD of {1, 1, 1, 5} and {1, 5, 5, 5} is same. Why? SD measures distance from mean. It has nothing to do with the actual value of mean and actual value of numbers. In {1, 1, 1, 5}, mean is 2. Three of the numbers are distance 1 away from mean and one number is distance 3 away from mean. In {1, 5, 5, 5}, mean is 4. Three of the numbers are distance 1 away from mean and one number is distance 3 away from mean.

Similarly, {1, 1, 3, 5} and {1, 3, 5, 5} will have the same SD.

Then, {1, 3, 3, 5} will have a distinct SD and {1, 1, 5, 5} will have a distinct SD. In all, there are 4 different values that SD can take in such a case.

Note: It doesn't matter what the actual numbers are. SD of 1, 3, 5, 7 is the same as SD of 12, 14, 16, 18. For detailed explanation of SD and how to calculate it, check the theory or Stats.

Thanks for the great explanations karishma, shrouded, and bunuel as always

E is a collection of four ODD integers and the greatest difference between any two integers in E is 4. The standard deviation of E must be one of how many numbers? (A) 3 (B) 4 (C) 5 (D) 6 (E) 7

Let the smallest odd integer be 1, thus the largest one will be 5. We can have following 6 types of sets:

CALCULATING STANDARD DEVIATION OF A SET {x1, x2, ... xn}: 1. Find the mean, \(m\), of the values. 2. For each value \(x_i\) calculate its deviation (\(m-x_i\)) from the mean. 3. Calculate the squares of these deviations. 4. Find the mean of the squared deviations. This quantity is the variance. 5. Take the square root of the variance. The quantity is th SD.

Expressed by formula: \(standard \ deviation= \sqrt{variance} = \sqrt{\frac{\sum(m-x_i)^2}{N}}\).

You can see that deviation from the mean for 2 pairs of the set is the same, which means that SD of 1 and 6 will be the same and SD of 2 and 5 also will be the same. So SD of such set can take only 4 values.

Answer: B.

Hope it's clear.

Hi, in the sets above why aren't sets [3,5,5,5] and [3,3,3,5] considered? Their is no limit on minimum range.

E is a collection of four ODD integers and the greatest difference between any two integers in E is 4. The standard deviation of E must be one of how many numbers? (A) 3 (B) 4 (C) 5 (D) 6 (E) 7

Let the smallest odd integer be 1, thus the largest one will be 5. We can have following 6 types of sets:

CALCULATING STANDARD DEVIATION OF A SET {x1, x2, ... xn}: 1. Find the mean, \(m\), of the values. 2. For each value \(x_i\) calculate its deviation (\(m-x_i\)) from the mean. 3. Calculate the squares of these deviations. 4. Find the mean of the squared deviations. This quantity is the variance. 5. Take the square root of the variance. The quantity is th SD.

Expressed by formula: \(standard \ deviation= \sqrt{variance} = \sqrt{\frac{\sum(m-x_i)^2}{N}}\).

You can see that deviation from the mean for 2 pairs of the set is the same, which means that SD of 1 and 6 will be the same and SD of 2 and 5 also will be the same. So SD of such set can take only 4 values.

Answer: B.

Hope it's clear.

Hi, in the sets above why aren't sets [3,5,5,5] and [3,3,3,5] considered? Their is no limit on minimum range.

This cases are not possible since "the greatest difference between any two integers in E is 4" means that the range of the set is 4. _________________

E is a collection of four ODD integers and the greatest difference between any two integers in E is 4. The standard deviation of E must be one of how many numbers? (A) 3 (B) 4 (C) 5 (D) 6 (E) 7

Let the smallest odd integer be 1, thus the largest one will be 5. We can have following 6 types of sets:

CALCULATING STANDARD DEVIATION OF A SET {x1, x2, ... xn}: 1. Find the mean, \(m\), of the values. 2. For each value \(x_i\) calculate its deviation (\(m-x_i\)) from the mean. 3. Calculate the squares of these deviations. 4. Find the mean of the squared deviations. This quantity is the variance. 5. Take the square root of the variance. The quantity is th SD.

Expressed by formula: \(standard \ deviation= \sqrt{variance} = \sqrt{\frac{\sum(m-x_i)^2}{N}}\).

You can see that deviation from the mean for 2 pairs of the set is the same, which means that SD of 1 and 6 will be the same and SD of 2 and 5 also will be the same. So SD of such set can take only 4 values.

Answer: B.

Hope it's clear.

Hi, in the sets above why aren't sets [3,5,5,5] and [3,3,3,5] considered? Their is no limit on minimum range.

This cases are not possible since "the greatest difference between any two integers in E is 4" means that the range of the set is 4.

I have seen that in all previous posts, consideration of sets that are all the same number such as [1,1,1,1] were not considered. Why is that?

Hi, in the sets above why aren't sets [3,5,5,5] and [3,3,3,5] considered? Their is no limit on minimum range.

This cases are not possible since "the greatest difference between any two integers in E is 4" means that the range of the set is 4.

I have seen that in all previous posts, consideration of sets that are all the same number such as [1,1,1,1] were not considered. Why is that?

The greatest difference between any two integers in E is 4 means that the range of the set is 4 and the range of {1, 1, 1, 1} is 0, not 4. _________________

Re: E is a collection of four ODD integers and the greatest [#permalink]

Show Tags

21 Jul 2014, 03:36

Expert's post

HarvinderSaini wrote:

Hi

Isn't a set with values 3,3,5, 7 viable??

Yes, it is.

The sets in my post are based on an assumption that the smallest integer is 1 to simplify finding a pattern. Your set is similar to {1, 1, 3, 5} in my solution. _________________

Excellent posts dLo saw your blog too..!! Man .. you have got some writing skills. And Just to make an argument = You had such an amazing resume ; i am glad...

So Much $$$ Business school costs a lot. This is obvious, whether you are a full-ride scholarship student or are paying fully out-of-pocket. Aside from the (constantly rising)...

I barely remember taking decent rest in the last 60 hours. It’s been relentless with submissions, birthday celebration, exams, vacating the flat, meeting people before leaving and of...

Rishabh from Gyan one services, India had a one to one interview with me where I shared my experience at IMD till now. http://www.gyanone.com/blog/life-at-imd-interview-with-imd-mba/ ...