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mean and sd

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by divya23 » Thu Jun 02, 2011 8:43 pm
The mean and standard deviation of 8 numbers are 10 and .3 resp.What % of the 8 numbers are within 1 s.d of the mean.
9.4,9.9,9.9,9.9,10.0.10.2,10.2,10.5
a.90%
b.80%
c.85%
d.75%
e.70%

[spoiler]OA = D[/spoiler]
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by Frankenstein » Thu Jun 02, 2011 8:48 pm
Hi,
Numbers within 1s.d of mean = numbers between (mean-s.d) and (mean+s.d) i.e. 10-0.3 and 10+0.3 =9.7,10.3 There are 6 elements out of 8 in this range.
So 6/8 = 75%

Hence, D
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by edvhou812 » Thu Jun 02, 2011 8:50 pm
Numbers within .3 of the mean: 9.9, 9.9, 9.9, 10, 10.2, 10.2. Number of integers .3 SD from the mean: 6.

6/8=.75

Answer: D
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by cans » Thu Jun 02, 2011 8:51 pm
mean=10,
s.d.=.3
within 1 s.d. of the mean means between 10-.3 to 10+.3
between 9.7 to 10.3
9.9,9.9,9.9,10.0,10.2,10.2
6/8 = 75%
IMO D
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by divya23 » Mon Jun 06, 2011 10:50 am
how will things change wen i say mean is 8.1 and s.d is .3
den v have to find numbers within 1.5 s.d of mean ???
plz xplain thank u
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by Frankenstein » Mon Jun 06, 2011 10:57 am
divya23 wrote:how will things change wen i say mean is 8.1 and s.d is .3
den v have to find numbers within 1.5 s.d of mean ???
plz xplain thank u
Hi,
I don't understand your query exactly. In the original question we are asked to find numbers with 1s.d. of the mean. That means the numbers in the range (mean-s.d, mean+s.d).
If the question asks to find numbers within 'n' s.d.s, it means numbers in the range (mean-n*s.d,mean+n*s.d).
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by divya23 » Mon Jun 06, 2011 11:01 am
the list is like
7.51
8.22
7.86 and dere are many oder numbers like dese
the q is mean of these numbers is 8.1 and s.d = .3 how many 12 listed are within 1.5 s.d of mean...

i just wanted to know d equation
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by Frankenstein » Mon Jun 06, 2011 11:18 am
divya23 wrote:the list is like
7.51
8.22
7.86 and dere are many oder numbers like dese
the q is mean of these numbers is 8.1 and s.d = .3 how many 12 listed are within 1.5 s.d of mean...

i just wanted to know d equation
Hi,
The basic concept is still the same as I mentioned in my prev post. substitute mean=8.1, s.d=0.3 and n=1.5.
So, the required range of the numbers is between (8.1-1.5*0.3) and (8.1+1.5*0.3) i.e. between 7.65 and 8.55.
Cheers!

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by aftableo2006 » Mon Jun 06, 2011 8:35 pm
between 1 standard deviation of the mean means between (x-SD) and (x+SD)here it between 9.7 to 10.3
there are 6 numbers out of 8 so the ans is 75% it is D
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