Consider the two confidence intervals for μ, the true average (i.e., population mean) resonance frequency (measured in Hz) for all tennis rackets of a certain type:

(114.4, 115.6) (114.1, 115.9)

(a) What is the value of the sample mean resonance frequency?

(b) Both intervals were calculated from the same sample data. The confidence level for one interval is 90%; the confidence level for the other interval is 99%. Which interval is the 90% confidence level, and why?