During the first half of 2013, it was discovered that British Columbia Hydro was dramatically overcharging customers in a Burnaby condominium complex. New “smart” meters had been installed but not...

During the first half of 2013, it was discovered that British Columbia Hydro was dramatically overcharging customers in a Burnaby condominium complex. New “smart” meters had been installed but not connected to units, and the company was estimating electricity use based on very poor comparisons.46 Suppose a random sample of bimonthly electricity bills for these condominium owners was obtained before and after the new meters were installed.

a. Find a 99% confidence interval for the population variance in electricity bills before the new meters were installed.

b. Find a 99% confidence interval for the population variance in electricity bills after the new meters were installed.

c. Is there any evidence to suggest that the variance is different before and after the new meters were installed? Justify your answer.

Given a random sample of size n from a normal population with variance a2 :

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