2. Each of the following is a con dence interval for m  true average (i.e., population mean) resonance frequency (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 con dence level for one of these intervals is 90% and for the other is 99%. Which of the intervals has the 90% con dence level, and why?

x  1.44s/1n x  2.81s/1n