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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?


What assumptions are made?

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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.

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