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Mean and Median

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by clock60 » Wed Aug 11, 2010 3:13 am
seems like 12
20+3*2.5=27.5
20-3*2,5=12,5
the only number that out of range 12,5<x<27,5. is 12
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by albatross86 » Wed Aug 11, 2010 3:15 am
1 standard deviation = 3
2 standard deviations = 3*2 = 6
2.5 standard deviations = 3*2.5 = 7.5

Standard deviation represents the average deviation of all members of the set from the mean of that set. This means that we are looking for a number that is more than 7.5 units away from 20.

=> 12 (which is 8 units away) Pick A.
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by sheelanadh » Wed Aug 11, 2010 4:19 am
albatross86 wrote:1 standard deviation = 3
2 standard deviations = 3*2 = 6
2.5 standard deviations = 3*2.5 = 7.5

Standard deviation represents the average deviation of all members of the set from the mean of that set. This means that we are looking for a number that is more than 7.5 units away from 20.

=> 12 (which is 8 units away) Pick A.

thank u .... please explain me in little bit clarity....
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by beatthegmatinsept » Wed Aug 11, 2010 7:59 am
sheelanadh wrote:
albatross86 wrote:1 standard deviation = 3
2 standard deviations = 3*2 = 6
2.5 standard deviations = 3*2.5 = 7.5

Standard deviation represents the average deviation of all members of the set from the mean of that set. This means that we are looking for a number that is more than 7.5 units away from 20.

=> 12 (which is 8 units away) Pick A.

thank u .... please explain me in little bit clarity....
Given,
Mean = 20
SD = 3
For something to be 1 SD away from the mean, the number will be either greater than (20+3= 23) OR less than (20-3=17).
Using the same logic, for something to be 2 SD's away, the number will be either greater than (20+6+26) OR less than (20-6=14).
The question asks 2.5 SD. So, 2.5 SD = 2.5(3) = 7.5. SO your answer should be either greater than 27.5 OR less than 12.5. The only answer choice that meets that criteria is A.
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