The proper operation of typical home appliances requires voltage levels that do not vary much. Listed below are 6 voltage levels (in volts) at a random house on 6 different days.

119.9	120.1	120	120	120
119.9

The mean of the data set is 119.98; the sample standard deviation is 0.075; if the normality plot is not provided you may assume that the voltages are normally distributed.

Construct a 99% confidence interval for the variance (standard deviation) of all voltages in the house.

1. Procedure: Select an answer One proportion Z procedure One variance χ² procedure One mean Z procedure One mean T procedure
2. Assumptions: (select everything that applies)
   • Population standard deviation is known
   • Normal population
   • Simple random sample
   • Population standard deviation is unknown
   • The number of positive and negative responses are both greater than 10
   • Sample size is greater than 30
3. Unknown parameter: Select an answer σ², population variance p, population proportion μ, population mean