# If I know the population mean but want to determine the standard deviation for a trail of several events; should I be dividing by the number of events or the number of events minus 1?

## For example, I know the (true) population mean for the sum of 2 six-sided dice is 7. A series of 6 trials generated the results $\left\{4 , 11 , 6 , 9 , 12 , 7\right\}$. Should I use population variance and standard deviation, or sample variance and standard deviation? I seem to remember that the reduction of the divisor for a sample was because the sample mean was only an estimate of the true population mean, but hat isn't the case here.

If wanting the standard deviation from the mean of the model then you would divide by $n$.
If wanting the standard deviation of the data then you would divide by $n - 1$.