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Which of the following triples of numbers have the same

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Which of the following triples of numbers have the same  [#permalink]

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New post 01 Nov 2013, 07:08
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Which of the following triples of numbers have the same standard deviation as the numbers r, s, and t?

I. r-2, s-2, t-2
II. 0, r-s, t-s
III. r-4, s+5, t-1

A. I only
B. II only
C. I and II only
D. I and III only
E. I, II, and III

Please help me figure out II & III. Thanks!
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 01 Nov 2013, 07:16
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zbvl wrote:
Which of the following triples of numbers have the same standard deviation as the numbers r, s, and t?

I. r-2, s-2, t-2
II. 0, r-s, t-s
III. r-4, s+5, t-1

A. I only
B. II only
C. I and II only
D. I and III only
E. I, II, and III

Please help me figure out II & III. Thanks!


If we add or subtract a constant to each term in a set the standard deviation will not change.

Set {r-2, s-2, t-2} is obtained by subtracting 2 from each term of {r, s, t}.
Set {0, r-s, t-s} is obtained by subtracting s from each term of {r, s, t}.
Set {r-4, s+5, t-1} is totally different from {r, s, t}.

Thus the answer is I and II only.

Answer: C.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 01 Nov 2013, 07:23
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Bunuel wrote:
zbvl wrote:
Which of the following triples of numbers have the same standard deviation as the numbers r, s, and t?

I. r-2, s-2, t-2
II. 0, r-s, t-s
III. r-4, s+5, t-1

A. I only
B. II only
C. I and II only
D. I and III only
E. I, II, and III

Please help me figure out II & III. Thanks!


If we add or subtract a constant to each term in a set the standard deviation will not change.

Set {r-2, s-2, t-2} is obtained by subtracting 2 from each term of {r, s, t}.
Set {0, r-s, t-s} is obtained by subtracting s from each term of {r, s, t}.
Set {r-4, s+5, t-1} is totally different from {r, s, t}.

Thus the answer is I and II only.

Answer: C.


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Which of the following triples of numbers have the same  [#permalink]

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New post 06 Mar 2015, 01:04
zbvl wrote:
Which of the following triples of numbers have the same standard deviation as the numbers r, s, and t?

I. r-2, s-2, t-2
II. 0, r-s, t-s
III. r-4, s+5, t-1

A. I only
B. II only
C. I and II only
D. I and III only
E. I, II, and III

Please help me figure out II & III. Thanks!



SD is about finding the squareroot of the sum of difference of Avg of the numbers and the numbers individually. If we can find out the (Avg-Number) set same in given options then we can conclude that the SD is same.
In the above problem, the Avg of r,s,t is (r+s+t)/3 and the difference with each of the numbers are (s+t-2r)/3, (r+t-2s)/3 and (r+s-2t)/3. If you try to compute the difference in I & II sets, you will notice that the difference remains same for the sets.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 09 Mar 2016, 04:12
Her the rule is that the standard deviation does not change if we add or subtract same thing from all the numbers
Hence C
Also never ever make the mistake of choosing numbers here.
I used to do that ..
as some of them may satisfy the third case too..

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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 21 Aug 2016, 11:05
Bunuel: Please confirm - When there is a different constant added to a list of numbers, does the standard deviation change?
For example: a, b, and c have s.d. 'x'
Will a+3, b+7, c+3 have s.d. 'x'?
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 27 Aug 2016, 11:06
Keats wrote:
Bunuel: Please confirm - When there is a different constant added to a list of numbers, does the standard deviation change?
For example: a, b, and c have s.d. 'x'
Will a+3, b+7, c+3 have s.d. 'x'?


Adding or subtracting doesn't change the standard deviation while multiplying or dividing does.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 27 Aug 2016, 12:16
abhimahna wrote:
Keats wrote:
Bunuel: Please confirm - When there is a different constant added to a list of numbers, does the standard deviation change?
For example: a, b, and c have s.d. 'x'
Will a+3, b+7, c+3 have s.d. 'x'?


Adding or subtracting doesn't change the standard deviation while multiplying or dividing does.


Looks like you have not read my question clearly. I understand adding/subtracting doesn't effect s.d. But if I ask you to calculate s.d. for below

a) s+1, t + 6, u +4
b) s+1, t+ 1, u+ 1

when you know s.d. of s,t,u is d, what will be your answer?
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 27 Aug 2016, 12:52
Keats wrote:
abhimahna wrote:
Keats wrote:
Bunuel: Please confirm - When there is a different constant added to a list of numbers, does the standard deviation change?
For example: a, b, and c have s.d. 'x'
Will a+3, b+7, c+3 have s.d. 'x'?


Adding or subtracting doesn't change the standard deviation while multiplying or dividing does.


Looks like you have not read my question clearly. I understand adding/subtracting doesn't effect s.d. But if I ask you to calculate s.d. for below

a) s+1, t + 6, u +4
b) s+1, t+ 1, u+ 1

when you know s.d. of s,t,u is d, what will be your answer?



HI THERE..!
The Thing is => The stem has asked that when will the SD remain the same. It impliesSITUATIONS WHEN SD WILL BE SAME IRRESPECTIVE OF THE VALUE OF S,T,U

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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 27 Aug 2016, 14:45
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stonecold wrote:

HI THERE..!
The Thing is => The stem has asked that when will the SD remain the same. It impliesSITUATIONS WHEN SD WILL BE SAME IRRESPECTIVE OF THE VALUE OF S,T,U

Regards
Stone Cold


Thanks stonecold. As far as this question is concerned, I have no doubts. I just wanted to extend the learning and point that if we add/subtract same constant to r,s, and t there will be no change in the standard deviation and it will remain the same as that of r,s, and t.

However, if we add random constant to each r,s, and t then the standard deviation will definitely CHANGE. However, we will have to do calculation to it! So the case is that it should be the *same constant* that is added to r,s, and t.

I hope I am able to convey my point.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 27 Aug 2016, 15:14
Keats wrote:
abhimahna wrote:
Keats wrote:
Bunuel: Please confirm - When there is a different constant added to a list of numbers, does the standard deviation change?
For example: a, b, and c have s.d. 'x'
Will a+3, b+7, c+3 have s.d. 'x'?


Adding or subtracting doesn't change the standard deviation while multiplying or dividing does.


Looks like you have not read my question clearly. I understand adding/subtracting doesn't effect s.d. But if I ask you to calculate s.d. for below

a) s+1, t + 6, u +4
b) s+1, t+ 1, u+ 1

when you know s.d. of s,t,u is d, what will be your answer?


For a, standard deviation will change since different constant is added to each term.
For b, standard deviation will not change since same constant is added to each term.
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Which of the following triples of numbers have the same  [#permalink]

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New post 27 Aug 2016, 16:20
Keats wrote:
stonecold wrote:

HI THERE..!
The Thing is => The stem has asked that when will the SD remain the same. It impliesSITUATIONS WHEN SD WILL BE SAME IRRESPECTIVE OF THE VALUE OF S,T,U

Regards
Stone Cold


Thanks stonecold. As far as this question is concerned, I have no doubts. I just wanted to extend the learning and point that if we add/subtract same constant to r,s, and t there will be no change in the standard deviation and it will remain the same as that of r,s, and t.

However, if we add random constant to each r,s, and t then the standard deviation will definitely CHANGE. However, we will have to do calculation to it! So the case is that it should be the *same constant* that is added to r,s, and t.

I hope I am able to convey my point.




This Will clear Any Doubts you have Regarding Standard Deviation =>
math-standard-deviation-87905.html



Regards
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 27 Aug 2016, 22:54
Keats wrote:
abhimahna wrote:
Keats wrote:
Bunuel: Please confirm - When there is a different constant added to a list of numbers, does the standard deviation change?
For example: a, b, and c have s.d. 'x'
Will a+3, b+7, c+3 have s.d. 'x'?


Adding or subtracting doesn't change the standard deviation while multiplying or dividing does.


Looks like you have not read my question clearly. I understand adding/subtracting doesn't effect s.d. But if I ask you to calculate s.d. for below

a) s+1, t + 6, u +4
b) s+1, t+ 1, u+ 1

when you know s.d. of s,t,u is d, what will be your answer?


What I meant was adding or subtracting a constant term doesn't change the SD. Its like an AP, when you add or subtract a constant term to each o the term of an AP, it never changes.

Hence, in your options above, in a) you are adding a different rem to each of the terms, So SD will change

but in b) since you are adding a constant term to each of the terms, it would not have any impact.

I hope its clear now.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 28 Aug 2016, 00:10
Thanks abhimahna. Also thank you stonecold for sharing the standard deviation link. It is useful.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 20 Nov 2017, 19:32
In case of doubt, we can just put in a value and solve this question.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 22 Nov 2017, 01:31
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SD=difference of values from the mean(this is simplified definition but will serve the purpose)
Calculations are not required but we will do them to get the idea
Let r=10
s=15
t=20
mean=10+15+20/3=15
Difference of each value from mean
r
10-15=-5
s
15-15=0
t
20-15=5
let us look at answer choices
r-2=10-2=8
s-2=15-2=13
t-2=20-2=18
Average of new set=8+13+18/3=45/3=15
the difference from mean
r-2
8-13=-5
s-2
13-13=0
t-2
18-13=5
the difference is same as the 1st set and hence SD will be same.

2nd option
0
r-s=10-15=-5
t-s=20-15=5
this set contains 0,-5 and 5 same as 1st set.
hence answer is C.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 23 Nov 2017, 09:17
The rule is "the standard deviation of a set will not change If we add/ subtract a constant to each term in a set"
=> Sd of (r-2, s-2, t-2) = sd of (r,s,t) because set (r-2, s-2, t-2) obtained by subtract each term (r,s,t) by 2.
Sd of (0, r-s, t-s) = sd of (r,s,t) because set (o, r-s, t-s) obtained by subtract each term (r,s,t) by s.
Hence, the answer is C.
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 27 Nov 2017, 11:55
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zbvl wrote:
Which of the following triples of numbers have the same standard deviation as the numbers r, s, and t?

I. r-2, s-2, t-2
II. 0, r-s, t-s
III. r-4, s+5, t-1

A. I only
B. II only
C. I and II only
D. I and III only
E. I, II, and III



We may recall the rule that when we add or subtract the same constant to a set of numbers the standard deviation does not change. Let’s analyze each Roman Numeral:

I. r-2, s-2, t-2

Since 2 is subtracted from r, s, and t, the standard deviation is the same as that of r, s, and t.

II. 0, r-s, t-s

If we subtract s from r, s, and t, we have r - s, s - s = 0, and t - s, thus the standard deviation is the same as that of r, s, and t.

III. r-4, s+5, t-1

We see that since we subtract/add different numbers to r, s, and t, we do not have the same standard deviation as that of r, s, and t.

Answer: C
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Re: Which of the following triples of numbers have the same  [#permalink]

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New post 21 Aug 2018, 17:48
Hi Bunuel,
Is this question of Must be category or Could be category?
Its not explicitly mentioned in Question.
I am assuming it to be Must be Question. Is this understanding correct?
Thanks in advance! :-)
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Re: Which of the following triples of numbers have the same   [#permalink] 21 Aug 2018, 17:48
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