The service life of a battery used in a cardiac pacemaker is assumed to be normally distributed. A random sample of 10 batteries is subjected to an accelerated life test by running them continuously at an elevated temperature until failure, and the following lifetimes (in hours) are obtained: 25.5, 26.1, 26.8, 23.2, 24.2, 28.4, 25.0, 27.8, 27.3 and 25.7.

a) The manufacturer wants to be certain that the mean battery life exceeds 25h. What conclusions can be drawn from these data (use alpha = 0.05)

b) Construct a 90% two-sided confidence interval on mean life in the accelerated test.

a) The manufacturer wants to be certain that the mean battery life exceeds 25h. What conclusions can be drawn from these data (use alpha = 0.05)

b) Construct a 90% two-sided confidence interval on mean life in the accelerated test.

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