Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 29 Nov 2009
Posts: 25
Location: Bangalore  INDIA
Schools: Duke, NUS,Rutgers
WE 1: Health & Life Science

Questions about the standard deviation [#permalink]
Show Tags
01 Apr 2010, 23:19
5
This post was BOOKMARKED
1> if the mean of a data set is 75 and the standard deviation (SD) is 10, what is the range of scores that fall within one SD of the mean?
2> If y=ax+b, and if teh SD of x series is S, what is the SD of Y series?
3> If ax+by+c=0, and if the SD of X series is S, what is the SD of Y series?
4>If sets X and Y have an equal number of elements, does set X have a greater SD that set Y? a> The difference between each pair of the neighboring elements is consistent throughout each set.
b> Each of the first two elements in set Y is twics greater than the corresponding first and second elements is set X



Senior Manager
Joined: 01 Feb 2010
Posts: 264

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
02 Apr 2010, 10:02
divakarbio7 wrote: 1> if the mean of a data set is 75 and the standard deviation (SD) is 10, what is the range of scores that fall within one SD of the mean?
Lower Limit: 65 Upper Limit: 85 20 is range



Senior Manager
Joined: 01 Feb 2010
Posts: 264

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
02 Apr 2010, 10:06
2
This post was BOOKMARKED
divakarbio7 wrote: 2> If y=ax+b, and if teh SD of x series is S, what is the SD of Y series?
SD of y will be aS. Taking case if x is 0,1,2,3,4..... SD is S now for series 1,2,3,4,5....... SD is S still (SD remains same if we add same number in all digits) but for series 0,5,10,15,20,..... SD is 5S (SD becomes constant*OLD SD when all digits are multiplied by same constant).



Senior Manager
Joined: 01 Feb 2010
Posts: 264

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
02 Apr 2010, 10:07
1
This post received KUDOS
1
This post was BOOKMARKED
divakarbio7 wrote: 3> If ax+by+c=0, and if the SD of X series is S, what is the SD of Y series? y = a/b*x  c As per earlier logic SD of Y will be a/b(S).



Senior Manager
Joined: 01 Feb 2010
Posts: 264

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
02 Apr 2010, 10:11
divakarbio7 wrote: 4>If sets X and Y have an equal number of elements, does set X have a greater SD that set Y? a> The difference between each pair of the neighboring elements is consistent throughout each set.
b> Each of the first two elements in set Y is twics greater than the corresponding first and second elements is set X a: Not enough SD of both sets cannot be determined. b: Not enough SD of both sets cannot be determined. Combining, we can infer difference of X is (ba) then of Y is 2(ba) and it is consistent throughtout so SD can be calculated hence Sufficient so C.



Manager
Joined: 28 Aug 2009
Posts: 186

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
04 Apr 2010, 06:06
2
This post was BOOKMARKED
1> if the mean of a data set is 75 and the standard deviation (SD) is 10, what is the range of scores that fall within one SD of the mean? answer: 65 and 85 2> If y=ax+b, and if teh SD of x series is S, what is the SD of Y series? answer:SD OF Y series: aS 3> If ax+by+c=0, and if the SD of X series is S, what is the SD of Y series? answer:aS/b 4>If sets X and Y have an equal number of elements, does set X have a greater SD that set Y? a> The difference between each pair of the neighboring elements is consistent throughout each set.
b> Each of the first two elements in set Y is twics greater than the corresponding first and second elements is set X Answer: C



Intern
Joined: 19 Jun 2010
Posts: 12

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
19 Jul 2010, 18:40
4>If sets X and Y have an equal number of elements, does set X have a greater SD that set Y? a> The difference between each pair of the neighboring elements is consistent throughout each set.
b> Each of the first two elements in set Y is twics greater than the corresponding first and second elements is set X
ANSWER SHOULD BE E
1 1 1 2 2 2 meets both condition and SD(X)=SD(Y)



Intern
Joined: 23 Jun 2010
Posts: 24

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
28 Aug 2010, 23:24
agmatclubb wrote: 4>If sets X and Y have an equal number of elements, does set X have a greater SD that set Y? a> The difference between each pair of the neighboring elements is consistent throughout each set.
b> Each of the first two elements in set Y is twics greater than the corresponding first and second elements is set X
ANSWER SHOULD BE E
1 1 1 2 2 2 meets both condition and SD(X)=SD(Y) That's true .. still the ans should be "C" as both the statements are sufficient to answer the "Question" that "does set X have a greater SD than set Y?" as "NO" It doesn't matter whether X's SD is equal or less than Y's as long as it is not greater.



Joined: 31 Dec 1969
Location: Russian Federation
Concentration: Entrepreneurship, International Business
GMAT 3: 740 Q40 V50 GMAT 4: 700 Q48 V38 GMAT 5: 710 Q45 V41 GMAT 6: 680 Q47 V36 GMAT 9: 740 Q49 V42 GMAT 11: 500 Q47 V33 GMAT 14: 760 Q49 V44
WE: Supply Chain Management (Energy and Utilities)

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
01 Sep 2010, 18:53
For # 4, the answer should be A. Standard deviation depends on the differences between the elements regardless of the mean. These two sets meet the conditions of statement one and must have the same standard deviation: Set one: 2,4,6,8,10 Set two: 19, 21, 23, 25, 27 Statement 2 does not tell us about elements in each set beyond the 2nd element.



Manager
Joined: 11 Feb 2011
Posts: 134

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
14 Jun 2011, 19:50
divakarbio7 wrote: 4>If sets X and Y have an equal number of elements, does set X have a greater SD that set Y? a> The difference between each pair of the neighboring elements is consistent throughout each set. b> Each of the first two elements in set Y is twics greater than the corresponding first and second elements is set X a: Not enough SD of both sets cannot be determined. b: Not enough SD of both sets cannot be determined. Combining, we can infer difference of X is (ba) then of Y is 2(ba) and it is consistent throughtout so SD can be calculated hence Sufficient so C. I did get the explanation.pls help .
_________________
target:810 out of 800!



VP
Status: There is always something new !!
Affiliations: PMI,QAI Global,eXampleCG
Joined: 08 May 2009
Posts: 1326

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
14 Jun 2011, 21:56
4 combining a and b sets can be (1,2,3) and (2,4,6) or (1,1,1) and (2,2,2). thus giving different SD's. hence E it is.
_________________
Visit  http://www.sustainablesphere.com/ Promote Green Business,Sustainable Living and Green Earth !!



Director
Status: Prep started for the nth time
Joined: 29 Aug 2010
Posts: 684

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
15 Jun 2011, 09:11
For 3
3> If ax+by+c=0, and if the SD of X series is S, what is the SD of Y series?
Ans should be a/b * S as SD cannot be negative. Please correct me if i am wrong.
Crick



GMAT Tutor
Joined: 24 Jun 2008
Posts: 1179

Re: Standard Deviation !!!!  Please explain [#permalink]
Show Tags
15 Jun 2011, 11:53
These questions are all terribly worded. My best advice is just to skip them. The first question misuses the word 'range' (the range is the difference between the largest and smallest numbers in a set; they mean to ask for the interval of scores which are within one standard deviation of the mean); the second and third questions misuse the word 'series' (a series in mathematics is a sum, and we take the standard deviation of sets, not of sums), and regardless those questions make no mathematical sense. The GMAT will never test standard deviation in the way these questions are attempting to test it. I discussed what those questions are attempting to ask in a different post, and explained what takeaways are actually useful on the GMAT (scroll way down): plsexplainthemfrnds110985.htmlThe fourth question is ambiguous. First, sets are not in any order, so it makes no sense to talk about the 'first element' in a set. We also don't say 'twice greater' (technically that means 'three times as much', but you would never see that phrase on the GMAT); we just say 'twice'. Finally, in Statement 1, when they say 'consistent', it's not clear what that means. I think they mean to say that each set is equally spaced, in which case they should use the word 'equal', not 'consistent'. I'm not sure where these questions are from, but if the original source contains questions like these, it will be more confusing than helpful to use it for your preparation.
_________________
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



Manager
Joined: 11 Dec 2011
Posts: 54
Location: Malaysia
Concentration: Nonprofit, Sustainability
GPA: 3.16
WE: Consulting (Computer Software)

Re: 1> if the mean of a data set is 75 and the standard [#permalink]
Show Tags
17 Jan 2012, 01:50
Sorry to bring up an old topic, just wanted to clarify some things. For question 2, can I assume that a constant added value will never change the value of the SD?



Math Expert
Joined: 02 Sep 2009
Posts: 39723

Re: 1> if the mean of a data set is 75 and the standard [#permalink]
Show Tags
17 Jan 2012, 02:46
calvin1984 wrote: Sorry to bring up an old topic, just wanted to clarify some things. For question 2, can I assume that a constant added value will never change the value of the SD? Yes, if we add (or subtract) a constant to each term in a set: Mean will increase (or decrease) by the same constant. SD will not change.For example: if the standard deviation of set A={1, 11, 15} is d then the standard deviation of the following sets B={6, 16, 20} and C={0, 10, 14} is also d (set B obtained by adding 5 to each of the element of set A and set C is obtained by subtracting 1 to each of the element of set A). On the other hand if we increase or decrease each term in a set by the same percent (multiply by some constant): Mean will increase or decrease by the same percent. SD will increase or decrease by the same percent.For example: if the standard deviation of set A={1, 11, 15} is d then the standard deviation of the following sets B={2, 32, 30} is 2d (set B obtained by multiplying each of the element of set A by 2 (increasing by 100%)). More tips on SD: psquestionsaboutstandarddeviation85897.html (collection of PS questions on SD) latelymanyquestionswereaskedaboutthestandard85896.html (collection of DS questions on SD)
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Senior Manager
Joined: 07 Nov 2009
Posts: 305

3 similar questions on SD [#permalink]
Show Tags
31 Jan 2012, 00:20
3 similar questions on SD:
If y = ax + b, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
If ax + by + c = 0, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
If y = x – 100, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
Dont have the OA's.



Math Expert
Joined: 02 Sep 2009
Posts: 39723

Re: 3 similar questions on SD [#permalink]
Show Tags
31 Jan 2012, 01:42
rohitgoel15 wrote: 3 similar questions on SD:
If y = ax + b, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
If ax + by + c = 0, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
If y = x – 100, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
Dont have the OA's. Merging similar topics. Note that those are not quality questions as Ian notes above, so I wouldn't worry about them at all. See above post for some tips on SD (which are related to these questions). Generally for the GMAT you only need to understand the concept of SD: you won't be asked to actually calculate the standard deviation of a set on the GMAT. So, what is the main thing you should know about it? Standard deviation shows how much variation there is from the mean, how widespread a given set is. So, a low standard deviation indicates that the data points tend to be very close to the mean, whereas high standard deviation indicates that the data are spread out over a large range of values.Check this for more: mathstandarddeviation87905.html PS questions on SD: psquestionsaboutstandarddeviation85897.htmlDS questions on SD: dsquestionsaboutstandarddeviation85896.htmlHope it helps. Hope it helps.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Manager
Joined: 16 Jul 2011
Posts: 67
Location: India
GPA: 3.7
WE: Sales (Other)

Re: 3 similar questions on SD [#permalink]
Show Tags
16 Aug 2012, 06:17
rohitgoel15 wrote: 3 similar questions on SD:
If y = ax + b, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
If ax + by + c = 0, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
If y = x – 100, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
Dont have the OA's. Can anyone help with solution for this problem: If y = x – 100, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
_________________
My Road to an MBA  http://mbahopeful.wordpress.com



Intern
Joined: 18 Jan 2013
Posts: 8
GPA: 3.71

Re: 3 similar questions on SD [#permalink]
Show Tags
02 Aug 2013, 14:28
AVbyT wrote: rohitgoel15 wrote: 3 similar questions on SD:
If y = ax + b, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
If ax + by + c = 0, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
If y = x – 100, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series?
Dont have the OA's. Can anyone help with solution for this problem: If y = x – 100, and if the standard deviation of x series is ‘S’, what is the standard deviation of y series? here, you are deducting the same number 100 from each number of the series x. So, when you add or deduct the constant from all the numbers of a series, there is no change in the SD. So, the standard deviation remains S.




Re: 3 similar questions on SD
[#permalink]
02 Aug 2013, 14:28







