What is the x and y intercepts 10-2 y=20x

Pulling out like terms :

 1.1     Pull out like factors :

   10 - 2y - 20x  =   -2 • (y + 10x - 5) 

Equation at the end of step  1  :Step  2  :Equations which are never true :

 2.1      Solve :    -2   =  0

This equation has no solution.
A a non-zero constant never equals

The population size of the above data is 8, that is N=8
The mean (average) = (12 +10+ 11.5 +11.5 +12 +9 +9 +11)/8
                                 = 10.75
Standard deviation is the square root of variance, it is one of the measures of central dispersion, that is a measure of by how much the values in the data set are likely to differ from the mean. 
In this case, Standard deviation, s= √(∑(x-m)²)/(n-1)
                                                  = 1.172 
Thus, best approximation of the standard deviation is 1.17