The proper operation of web-based applications on a phone requires broadband speeds that do not vary much. Listed below are 30 broadband speeds (in Mbps) measured on 30 different days.

136.6	143.5	116.4	134.9	151.2
172	146.7	135.5	141.9	145.5
145	130	146.4	110.1	159.4
150.5	142.8	149.2	119.5	175.7
118	163.6	196.6	138.1	166
138.7	173.2	133.9	170.2	150.4

The mean of the data set is 146.72; the sample standard deviation is 19.406; if the normality plot is not provided you may assume that the broadband speeds are normally distributed.

Construct a 99% confidence interval for the variance (standard deviation) of broadband speed for the service provider.

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