# Confidence Intervals

How can we calculate $90\%$ confidence intervals for the variance and standard deviation of the concentration of artificial food colouring in different lots of colouring, given a random sample of $12$ lots, which yielded the following concentration values?

$0.013,0.016,0.009,0.018,0.014,0.010,0.013,0.014,0.012,0.014,0.015,0.010$

If you assume that the concentration is randomly distributed with mean $\mu$ and standa deviation $\sigma$, then you can use the same method as in this example.