It’s the third one.. I think
Calculate for the mean/ average of the given numbers:
μ = (1 + 2 + 3 + 4 + 5) / 5 = 3
Then, we calculate for the summation of the squares of differences of these numbers from the mean, S
S = (1 - 3)² + (2 - 3)² + (3 - 3)² + (4 - 3)² + (5 - 3)²
S = 10
Divide this summation by the number of items and take the square root of the result to get the standard deviation.
SD = sqrt (10 / 5) = sqrt 2
SD = 1.41
Thus, the standard deviation of the given is equal to 1.41.
The value for n is 
<h3>solving for n</h3>
<u>given data</u>
10n^{2} - 12 = -8
making n the subject of the formula
10n^{2} = -8 + 12
10n^{2} = 4
divide through by 10
n^{2} = 4 / 10
finding the square root of both sides
n = square root ( 4 / 10 )

n = 0.632 or 
Read more the subject of formula here: brainly.com/question/21140562
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