STD : Quant Question Archive [LOCKED]
Check GMAT Club App Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 04 Dec 2016, 02:23

### GMAT Club Daily Prep

#### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# STD

Author Message
Senior Manager
Joined: 19 Sep 2004
Posts: 369
Followers: 1

Kudos [?]: 5 [0], given: 0

### Show Tags

24 Dec 2004, 23:16
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

Hi guys!

Q) In two companies, the range of the member's salary is different. The range of company A is 60,000 and of B, is 30,000. Which company's deviation is greater?
1) The two companies have a same average salary $30,000. 2) The highest salary of A is 90,000. The highest salary of B is 60,000 support ur answers with reasoning. Thanks Saurabh Malpani Manager Joined: 28 Nov 2004 Posts: 76 Followers: 1 Kudos [?]: 0 [0], given: 0 [#permalink] ### Show Tags 25 Dec 2004, 13:50 swath20 wrote: I think its A I pick A as well We need to know the mean or average to answer this question. I. Gives the mean of both companies, since the mean of B is the range of B, the spread (STD) of the salary data of B is narrow compared with A. Sufficient. II. Gives the highest salary of A & B, thus given the range the lowest salary of both companies can be found BUT we are interested in the mean to answer the question and this stem does not provide that information. Insufficient. Intern Joined: 19 Aug 2004 Posts: 47 Followers: 1 Kudos [?]: 6 [0], given: 0 [#permalink] ### Show Tags 25 Dec 2004, 16:11 What we need is the average/arithmetic mean. This is provided to us in statement 1. This, together with, the range from the question stem is enough to answer the question. Therefore, the answer is A. VP Joined: 25 Nov 2004 Posts: 1493 Followers: 7 Kudos [?]: 96 [0], given: 0 Re: STD [#permalink] ### Show Tags 25 Dec 2004, 16:56 saurabhmalpani wrote: Hi guys! Q) In two companies, the range of the member's salary is different. The range of company A is 60,000 and of B, is 30,000. Which company's deviation is greater? 1) The two companies have a same average salary$30,000.
2) The highest salary of A is 90,000. The highest salary of B is 60,000

Thanks
Saurabh Malpani

the value of SD depends upon number of observations and the value of fluctuations i.e. we can say range. all other things being equal, the higher the range, the greater the SD. similarly, higher the number of observations, lower the SD.

from i, it can be said that these two companies have same mean, therefore the company A has higher SD over company B.

from ii, we can not estimate the SD.

therefore, OA is A.
Director
Joined: 07 Nov 2004
Posts: 689
Followers: 6

Kudos [?]: 142 [0], given: 0

### Show Tags

03 Jan 2005, 12:13
Quote:
Q) In two companies, the range of the member's salary is different. The range of company A is 60,000 and of B, is 30,000. Which company's deviation is greater?
1) The two companies have a same average salary $30,000. 2) The highest salary of A is 90,000. The highest salary of B is 60,000 Is there a typo in the question? If you combine statements 1 and 2, you have 1) average of A = average of B = 30,000 2) Lowest salary of A = lowest salary of B = 30,000 How can you have an average of 30,000 if the lowest number is 30,000 and the highest is 90,000 or 60,000. the average has to be greater than 30,000 Am I missing something in this question?? Also from this thread below it looks like you cannot predict SD from range and average... can someone explain? http://www.gmatclub.com/phpbb/viewtopic.php?t=11900&highlight=deviation Intern Joined: 09 Dec 2004 Posts: 6 Followers: 0 Kudos [?]: 0 [0], given: 0 [#permalink] ### Show Tags 03 Jan 2005, 12:57 I agree with gayathri...something wrong with the question Director Joined: 27 Dec 2004 Posts: 905 Followers: 1 Kudos [?]: 43 [0], given: 0 [#permalink] ### Show Tags 03 Jan 2005, 12:59 (E). Though we are given th mean, the range and the smallest as well as laargest salary, i think those are not sufficient to compute the standard deviation considering we do not 1. the number of employees each company has 2. the specific salary of each employee (data point). REcall that deviation is the measure of variation between the mean and each data point. i could be wrong though because this is GMAT so i look forward to the OA Senior Manager Joined: 19 Sep 2004 Posts: 369 Followers: 1 Kudos [?]: 5 [0], given: 0 [#permalink] ### Show Tags 03 Jan 2005, 14:42 Hi guys OA is A. I am sorry for the delay Thanks GMAT Club Legend Joined: 15 Dec 2003 Posts: 4302 Followers: 38 Kudos [?]: 417 [0], given: 0 [#permalink] ### Show Tags 04 Jan 2005, 15:43 gayathri wrote: Quote: Q) In two companies, the range of the member's salary is different. The range of company A is 60,000 and of B, is 30,000. Which company's deviation is greater? 1) The two companies have a same average salary$30,000.
2) The highest salary of A is 90,000. The highest salary of B is 60,000

Is there a typo in the question? If you combine statements 1 and 2, you have
1) average of A = average of B = 30,000
2) Lowest salary of A = lowest salary of B = 30,000

How can you have an average of 30,000 if the lowest number is 30,000 and the highest is 90,000 or 60,000. the average has to be greater than 30,000

Am I missing something in this question??

Also from this thread below it looks like you cannot predict SD from range and average... can someone explain?
http://www.gmatclub.com/phpbb/viewtopic.php?t=11900&highlight=deviation

Hi gayathri, The difference between this question and the one you provided the link to is that in this one, you are provided with the range and the SAME averages. At least, this is what you get as piece of information from stem and A. When you have SAME averages AND the ranges are given, you can find the SD around the mean. Consider my attachment below. A says that the average is 30, represented by the red square. The range is represented by the size of the box; 60 for CorpA and 30 for CorpB. Now, knowing that the average is 30 AND the range is 60 for A, we know that the SD for CorpA is then 30(+/-30 around the mean). For B, since the average is 30 AND the range is 30, we know that the SD is then 15(+/-15 around the mean). Hence, SD for CorpA is larger than SD for CorpB. A is sufficient.

Looking at only statement B, All we know are the highest salaries AND the range. The range being represented by the boxes does not change. What changes here is that we have the right hand side of the boxes touching 90 for CorpA and the 60 for CorpB. Their respective left hand sides will then be at 30 for both Corporations. However, does that mean that the SD will be +/-30, as previously explained, for CorpA and +/-15 for CorpB? Answer is NO because even the ranges are given, we do not know the mean, or in other words, the distribution of the individual data within that given range. Let's say we have a company of 3 employees for CorpA. The first one makes 30 and the second one makes 90. If the third employee makes 60, then the average will be 60 for CorpA but if the third employee makes 30, then the average will be (30+30+90)/3 = 50! Hence, the average can fluctuate because it is not given. If the average fluctuates, we will not know what the SD is for sure. So B is not sufficient.

Re-read carefully the link that you gave me and you will see that in that question, although the ranges are given, the averages are NOT same so it is not possible to compare the two and come to a conclusion. SD is one of the tough concepts to explain but which you have to read about on your own time in some college math or stats books. I would say that this is a highly likely GMAT question so make sure you understand the nuance between the "creative" ways in which ETS can ask you this.
_________________

Best Regards,

Paul

Last edited by Paul on 21 Jan 2005, 11:02, edited 1 time in total.
GMAT Club Legend
Joined: 15 Dec 2003
Posts: 4302
Followers: 38

Kudos [?]: 417 [0], given: 0

### Show Tags

04 Jan 2005, 15:45
Hmmm, I just noticed you cannot put attachments anymore. I will wait for the server transfer to be done and will post my attachment to the previous message to ease your understanding
_________________

Best Regards,

Paul

Director
Joined: 07 Nov 2004
Posts: 689
Followers: 6

Kudos [?]: 142 [0], given: 0

### Show Tags

04 Jan 2005, 16:54
Thanks for detailed explanation Paul! I did go back and refer to the link and I think I see what you are saying. I will wait the attachment.
Manager
Joined: 15 Jul 2004
Posts: 75
Location: London
Followers: 1

Kudos [?]: 0 [0], given: 0

### Show Tags

07 Jan 2005, 06:23
Guys, can we discuss this one a bit more?

I donâ€™t see why A is the OA. I totally agree with Folaa3, standard deviation gives a measure of how the data is arranged around the mean.

For Co. A the range is 60K, but it could be that there is only 1 salary 30K less than the mean (the sandwich boy, or the janitor) and 1 salary 30K greater than the mean (the CEO), but then lots of employees can have the salary exactly on the mean or very close to it. Then the STD will be very small. For Co. B, it could happen than the salaries are scattered around with lots of employees with salaries quite far away from the mean (Lots of low salaries and lots of high salaries, but few around the mean). Then Co. B will have a relatively large STD, bigger than Co. A.

But it could happen the opposite, salaries in A scattered and far from the mean, and salaries for B very close to the mean.

Letâ€™s assume companies have 10 employees:

salaries for A (in â€˜000s): 15, 43, 44, 44, 45, 45, 46, 46, 47, 75.
Range 60, average: 45
STD for A: 14.18

Salaries for B (in â€˜000s): 25, 25, 26, 26, 27, 52, 53, 54, 54, 55
Range: 30, average: 38.11
STD for B: 14.63

But:

salaries for A (in â€˜000s): 15, 25, 30, 35, 45, 45, 55, 60, 65, 75.
Range 60, average: 45
STD for A: 19.00

Salaries for B (in â€˜000s): 25, 27, 29, 30, 31, 32, 35, 40, 50, 55
Range: 30, average: 35.4
STD for B: 9.99

(STD calculated using the Windows XP calculator)

Statement 2 doesnâ€™t change anything, so I think the answer is E. Can anybody explain why is A, and give examples, please?
GMAT Club Legend
Joined: 15 Dec 2003
Posts: 4302
Followers: 38

Kudos [?]: 417 [0], given: 0

### Show Tags

21 Jan 2005, 11:04
Hi, just wanted to give you and update since we can now post attachments. See my explanation on SD with the attached diagram
_________________

Best Regards,

Paul

Manager
Joined: 06 Sep 2004
Posts: 69
Followers: 1

Kudos [?]: 0 [0], given: 0

### Show Tags

21 Jan 2005, 11:30
A can definitely NOT be the answer.
SVP
Joined: 03 Jan 2005
Posts: 2243
Followers: 16

Kudos [?]: 320 [0], given: 0

### Show Tags

21 Jan 2005, 11:39
It's E.

Standard deviation depends on how each individule data is located. Range only give you the difference between minimum and maximum.

Look at this example:

1 2 3 4 5
1 3 3 3 5
Both have same range and same avg. But the SD is definitely different. I is not sufficient. Neither is B.
Director
Joined: 19 Nov 2004
Posts: 559
Location: SF Bay Area, USA
Followers: 4

Kudos [?]: 190 [0], given: 0

### Show Tags

21 Jan 2005, 21:57
I thought so as soon as looked at the question.
I pick E.
My reasoning is:
Regardless of what the range is, we have no information about how the salaries are clustered around the mean in the two companies.
It is possible the two salaries, the largest and the smallest could be far away from the mean, but rest of the salaries could be closer to the mean, thereby reducing the SD.
Director
Joined: 14 Jul 2004
Posts: 700
Followers: 1

Kudos [?]: 40 [0], given: 0

### Show Tags

16 Sep 2005, 05:18
Isnt this a bad question? How can the Lowest value of A [30,000] be equal to the mean [30,000] if the higest value is 90,000.

The same applies for B. How can the lowest value of B[30,000] be equal to the mean [30,000] if the highest value is 60,000
VP
Joined: 22 Aug 2005
Posts: 1120
Location: CA
Followers: 1

Kudos [?]: 100 [0], given: 0

### Show Tags

16 Sep 2005, 11:00
artabro wrote:
Guys, can we discuss this one a bit more?
Letâ€™s assume companies have 10 employees:

salaries for A (in â€˜000s): 15, 43, 44, 44, 45, 45, 46, 46, 47, 75.
Range 60, average: 45
STD for A: 14.18

Salaries for B (in â€˜000s): 25, 25, 26, 26, 27, 52, 53, 54, 54, 55
Range: 30, average: 38.11
STD for B: 14.63

But:

salaries for A (in â€˜000s): 15, 25, 30, 35, 45, 45, 55, 60, 65, 75.
Range 60, average: 45
STD for A: 19.00

Salaries for B (in â€˜000s): 25, 27, 29, 30, 31, 32, 35, 40, 50, 55
Range: 30, average: 35.4
STD for B: 9.99

(STD calculated using the Windows XP calculator)

Statement 2 doesnâ€™t change anything, so I think the answer is E. Can anybody explain why is A, and give examples, please?

A.

Although your points are valid, if you start putting numbers you get property something like this:

"For data with approximately the same mean, the greater the range, the greater the standard deviation. "

In the examples you gave, you missed the point that A says "mean is same"

artabro wrote:
For Co. B, it could happen than the salaries are scattered around with lots of employees with salaries quite far away from the mean (Lots of low salaries and lots of high salaries, but few around the mean). Then Co. B will have a relatively large STD, bigger than Co. A.

In this case, the mean itself would be larger for Co B.
SVP
Joined: 03 Jan 2005
Posts: 2243
Followers: 16

Kudos [?]: 320 [0], given: 0

### Show Tags

17 Sep 2005, 11:51
duttsit wrote:
"For data with approximately the same mean, the greater the range, the greater the standard deviation. "

This is WRONG.

Let me give you a simple example:

Set A: 1 1 3 5 5
mean=3, range=4, std=2
Set B: 1 2 3 3 6
mean=3, range=5, std=1.87

The range only gives information about the max and min, but std is affected by every element that is included in the set.

Note that for GMAT you don't have to know how to calculate std.
_________________

Keep on asking, and it will be given you;
keep on seeking, and you will find;
keep on knocking, and it will be opened to you.

Manager
Joined: 28 May 2004
Posts: 65
Location: Kiev, Ukraine - Atlanta, GA
Followers: 2

Kudos [?]: 1 [0], given: 0

### Show Tags

17 Sep 2005, 16:20
hehe, guess where i've seen this question before

Go to page    1   2    Next  [ 28 posts ]

Display posts from previous: Sort by