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 350,000 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:

Re: Standard deviation problem [#permalink]
02 Jul 2011, 14:05

ruturaj wrote:

If Q is a set of consecutive integers, what is the standard deviation of Q?

(1) Set Q contains 21 terms.

(2) The median of set Q is 20.

st 2. median = 20 set = {19,20,21} or set = {18,19,20,21,22} => different deviations...so not sufficient

st 1 : set has 21 elements...so my median = mean = a22/2 = a11

for deviation formula is (sum of|ai-mean|)/n

here we know n=21 mean = a10 since they are consecutive integers |a1-a2|=1 so we |a11-a1|=10 similiarly all deciations can be found...squared and divided...so we will get a proper answer...therefore statement 1 is conclusive and sufficient!

hope it helps

also, study the Gmatclub notes on standard deviation in Gmat book _________________

It matters not how strait the gate, How charged with punishments the scroll, I am the master of my fate : I am the captain of my soul. ~ William Ernest Henley

i have placed unwanted (dot)s in between cuz i cant post links...havent been a member for five days...but thats the address for the open source book....go to the standard deviation section...very nice...all inclusive...you wont need to refer a second source. _________________

It matters not how strait the gate, How charged with punishments the scroll, I am the master of my fate : I am the captain of my soul. ~ William Ernest Henley

Re: Standard deviation problem [#permalink]
03 Jul 2011, 03:57

Expert's post

If you know all of the distances within a set, you can always find its standard deviation, since standard deviation is only based on the distances from each element to the average. So if you have a set of 21 consecutive integers, you can always find the standard deviation; you don't need to know how big these integers are.

If it's not clear why that's true, you can let M be the average of your 21 consecutive integers (M is also the median since our set is equally spaced). Then your set is:

and you can see that we know all of the distances from each element to M; those distances are 10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, and 10. Those are the numbers you need to compute standard deviation. _________________

GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Re: Standard deviation problem [#permalink]
05 Jul 2011, 05:22

it means that in an ordered set the mean is always the middle number ie for a set with 21 elements, the middle element is the (21+1)/2 element ie a11

my GMAT was today. got shredded in verbal. 34 quants was decent 48 680 in all _________________

It matters not how strait the gate, How charged with punishments the scroll, I am the master of my fate : I am the captain of my soul. ~ William Ernest Henley

Re: Standard deviation problem [#permalink]
05 Jul 2011, 05:51

Expert's post

fivedaysleft wrote:

it means that in an ordered set the mean is always the middle number ie for a set with 21 elements, the middle element is the (21+1)/2 element ie a11

You mean to say that in an 'equally spaced' set, the mean and median are equal. There's no such thing as an 'ordered set'; sets are not in any order (if a list of numbers is in order, it's a sequence, not a set). _________________

GMAT Tutor in Toronto

If you are looking for online GMAT math tutoring, or if you are interested in buying my advanced Quant books and problem sets, please contact me at ianstewartgmat at gmail.com

Re: Standard deviation problem [#permalink]
05 Jul 2011, 06:15

IanStewart wrote:

fivedaysleft wrote:

it means that in an ordered set the mean is always the middle number ie for a set with 21 elements, the middle element is the (21+1)/2 element ie a11

You mean to say that in an 'equally spaced' set, the mean and median are equal. There's no such thing as an 'ordered set'; sets are not in any order (if a list of numbers is in order, it's a sequence, not a set).

acknowledged. My bad _________________

It matters not how strait the gate, How charged with punishments the scroll, I am the master of my fate : I am the captain of my soul. ~ William Ernest Henley

Social entrepreneurs aren't running charities : ‘It’s easy to think about it in terms of charity: it’s not. They are sustainable, trading, revenue-generating businesses. The benefit of them...