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DS: STDs (m08q09) [#permalink]
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28 Nov 2008, 13:54
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This topic is locked. If you want to discuss this question please repost it in the respective forum. Set \(T\) consists of odd integers divisible by 5. Is standard deviation of \(T\) positive? 1. All members of \(T\) are positive 2. \(T\) consists of only one member Source: GMAT Club Tests  hardest GMAT questions On a side note, when a question tells you a set S has numbers x,y,z  do we assume that x y z will always be different numbers? or can they be the same number, but repeated 3 times. REVISED VERSION OF THIS QUESTION IS HERE: dsstdsm08q097334720.html#p1210600



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Re: DS: STDs (m08q09) [#permalink]
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02 Apr 2010, 12:16
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Statement 1 : All members of T are positive We have two possibilities here Case a) all the members are same => e.g T= {5,5,5} = {5} (Since by definition a 'Set' is a unique collection of objects.) => S.D = 0 Case b) all the members are different => e.g. T = {5,15,25} => S.D. = some positive number.Since statement 1 is giving two possibilities , its Not Sufficient Statement 2 : Set T consists of only one member => Since its only one member , S.D. =0Hence Statement 2 is Sufficient Hence the Answer is B
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Re: DS: STDs (m08q09) [#permalink]
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02 Apr 2010, 08:28
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B.
For A, we can't say that the SD will always be +ve as it can be 0 as in the case of B.



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Re: DS: STDs [#permalink]
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29 Nov 2008, 20:01
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i get B
SD of 1 object is 0



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Re: DS: STDs (m08q09) [#permalink]
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02 Apr 2010, 09:57
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bigfernhead wrote: Set \(T\) consists of odd integers divisible by 5. Is standard deviation of \(T\) positive? 1. All members of \(T\) are positive 2. \(T\) consists of only one member Source: GMAT Club Tests  hardest GMAT questions On a side note, when a question tells you a set S has numbers x,y,z  do we assume that x y z will always be different numbers? or can they be the same number, but repeated 3 times. 1: Not enough as all members can be same in that case SD is 0 which is not +ve but in other case when all numbers are +ve and different SD will be +ve hence insufficient. 2: Enough as SD is zero which is not +ve hence suffcient.



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Re: DS: STDs (m08q09) [#permalink]
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11 Apr 2013, 05:51
thaihoang305 wrote: snkrhed wrote: I'm not going to go into "how to solve" since many others are do it much better than I do.
I think for this question the key factors to know are: 1) definition of standard definition 2) definition of "0"
remember, when all numbers are the same or if there is one number in the set, the standard deviation is 0. 0 is not a positive integer. (positive integer is > 0). Sorry but is there some mistake here. Thought this helpful set of Bunuel mathnumbertheory88376.htmlThen positive number is a real number greater than 0 And 0 is not negative or positive number. Then in (2) SD = 0 => Why 0 is a positive number. I find out this revise of Bunuel dsstdsm08q097334720.html#p1210600He also says the answer is B. Could anyone here explain for me? From (2) we get that SD=0, thus the answer to the question "is SD positive" is NO, which makes the second statement sufficient.
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Re: DS: STDs [#permalink]
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28 Nov 2008, 16:27
Standard deviation is always postivie . It's a average distance from mean. Distance can't be negative
1  Suff 2 St dev is 0  Suff
D



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Re: DS: STDs [#permalink]
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28 Nov 2008, 19:53
Correct HG , SD is always positive
Also to answer the side note question
we cant assume that x y z will always be different numbers or they are the same number.



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Re: DS: STDs [#permalink]
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29 Nov 2008, 23:39
Did you type correctly? Y should be T, correct? "Set T consists of odd integers divisible by 5" and "T consists of only one member" in statement 2 are also inconsistant. 1: Anyway, statement 1 is not helpful in finding SD. 2: Statement 2 is definitely helps to get the SD, which is 0 in this case as the SD of an element is 0. bigfernhead wrote: Set Y consists of odd integers divisible by 5. Is standard deviation of T positive?
1) All members of T are positive 2) T consists of only one member
On a side note, when a question tells you a set S has numbers x,y,z  do we assume that x y z will always be different numbers? or can they be the same number, but repeated 3 times. For your side question, can you post the question if you have? Because a question with context would be very useful in anylizing the issue on hand. IMO, real gmat test do not offer such a confused context.
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Re: DS: STDs [#permalink]
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30 Nov 2008, 09:37
Yes, I made a small typo. The answer is B. However, isn't all STDs positive? so wouldn't A) answer the question "Is Standard deviation of T positive?" For the side note question, I posted the question in this link: 7p544767?t=73389#p544767Notice how X and Y even though different variables, can take on the same value (both x and y = 4), as per the OE in the post. I'm wondering if this is can be the case in the real GMAT. Btw, this was a gmat club test question. GMAT TIGER wrote: Did you type correctly? Y should be T, correct? "Set T consists of odd integers divisible by 5" and "T consists of only one member" in statement 2 are also inconsistant. 1: Anyway, statement 1 is not helpful in finding SD. 2: Statement 2 is definitely helps to get the SD, which is 0 in this case as the SD of an element is 0. bigfernhead wrote: Set Y consists of odd integers divisible by 5. Is standard deviation of T positive?
1) All members of T are positive 2) T consists of only one member
On a side note, when a question tells you a set S has numbers x,y,z  do we assume that x y z will always be different numbers? or can they be the same number, but repeated 3 times. For your side question, can you post the question if you have? Because a question with context would be very useful in anylizing the issue on hand. IMO, real gmat test do not offer such a confused context.



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Re: DS: STDs (m08q09) [#permalink]
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07 Apr 2010, 08:57
(1) 1: SD = 0; 1, 15, 15: SD = some +ve value............Insuff (2) 15: SD = 0; 15: SD = 0 as well. In all cases, for any single digit, SD = 0  NOT positive. Hence, B
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Re: DS: STDs (m08q09) [#permalink]
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14 Apr 2010, 02:43
The question is if it's positive or not. From both the statements we can make out if its positive or not. Stat 1: always +ve Stat 2: always 0  Not positive. So we can conclude both the statements alone are suffice. option D, Please let me know if im wrong.



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Re: DS: STDs (m08q09) [#permalink]
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14 Apr 2010, 02:54
gmatbull wrote: (1) 1: SD = 0; 1, 15, 15: SD = some +ve value............Insuff (2) 15: SD = 0; 15: SD = 0 as well. In all cases, for any single digit, SD = 0  NOT positive. Hence, B > odd integers divisible by 5 are 5,15,25,35,45 mean = 25 S.D = ((20^2 + 10^2 + 0^2 + 10^2 + 20^2) /5)^(1/2) which is always positive. case 2. say 5,15,25,35,45 mean = 13 S.D = +ve in any case. So option 1 is always +ve.



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Re: DS: STDs (m08q09) [#permalink]
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14 Apr 2010, 03:12
S1 is not sufficient. Consider Set T consisting of the same number elements ([4, 4, 4], for example). Then SD = 0. You can see more details in this post above: dsstdsm08q0973347.html?viewpost=709035#p709035kalrac wrote: The question is if it's positive or not. From both the statements we can make out if its positive or not. Stat 1: always +ve Stat 2: always 0  Not positive. So we can conclude both the statements alone are suffice. option D, Please let me know if im wrong.
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Re: DS: STDs (m08q09) [#permalink]
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06 Apr 2011, 05:10
The answer is B. (1) is insufficient as we don't know if all elements are same or different. (2) says there is only 1 element, so SD = 0, which is a definitive answer.
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Re: DS: STDs (m08q09) [#permalink]
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23 Apr 2011, 15:51
1. Not sufficient.
as we dont whether the elements of the set are same or diff
if same , SD =0 => is not greater than 0
if different , SD >0
2. Sufficient.
as there is only one element, SD =0.
Answer is B.



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Re: DS: STDs (m08q09) [#permalink]
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01 Jul 2011, 15:49
Terrific question...
Fell for the trap answer D....
Statement 1 presents a double case...It can be +ve or zero!
Brilliant question!



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Re: DS: STDs (m08q09) [#permalink]
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10 Apr 2012, 06:36
amod243 wrote: Statement 1 : All members of T are positive We have two possibilities here
Case a) all the members are same => e.g T= {5,5,5} = {5} (Since by definition a 'Set' is a unique collection of objects.) => S.D = 0
Case b) all the members are different => e.g. T = {5,15,25} => S.D. = some positive number.
Since statement 1 is giving two possibilities , its Not Sufficient
Statement 2 : Set T consists of only one member => Since its only one member , S.D. =0 Hence Statement 2 is Sufficient
Hence the Answer is B Best answer to a tricky question! Fell into the trap and didn't consider the difference between 'positive' and positive or null'... This one goes on my error log.
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Re: DS: STDs (m08q09) [#permalink]
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10 Apr 2012, 06:55
Answer was A than after reading explanation of amod243 now my answer is B. nice explanation....



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Re: DS: STDs (m08q09) [#permalink]
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10 Apr 2012, 09:59
I think language for 1 is not clear. It can be zero or +ve.
For 2 always zero
So B it is




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