A soft drink machine is regulated so that the amount of drink it dispenses follows a normal distribution with a known standard deviation, and it is believed that standard deviation of the drinks dispensed is 20 milliliters.
However a random sample of 30 drinks from the machine produced an average value of 373 milliliters and standard deviation of 23.4 milliliters; therefore, based on the results from sample data, there is concern that population standard deviation might be higher than what is believed.

Question

A soft drink machine is regulated so that the amount of drink it dispenses follows a normal distribution with a known standard deviation, and it is believed that standard deviation of the drinks dispensed is 20 milliliters. 
However a random sample of 30 drinks from the machine produced an average value of 373 milliliters and standard deviation of 23.4 milliliters; therefore, based on the results from sample data, there is concern that population standard deviation might be higher than what is believed.

anonymous · Answer

Check the validity of the concern by determining a 95% confidence interval for the standard deviation of all drinks dispensed by this machine.

ganeshie8 · Answer

Oh its not about mean, its asking CI for population std dev
@amistre64

amistre64 · Answer

there are different distributions like X^2, F, and the like that are generally used when determing a particular parameter.  If memory serves, the X^2 relates to sds ... maybe.