# Estimation of standard deviation

A study of annual growth of cacti indicated $64$ of them, selected at random, had a mean annual growth of $52.80$ mm with a standard deviation of $4.5$ mm. Construct a $99$% confidence interval for the standard deviation of the annual growth.

My book has nothing on estimating standard deviation. I know variance uses the chi square table so I thought if I took the square root of the variance, I could get standard deviation. However, the table in the back of my book does not go to $64$. :(

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