Question

Construct a 99% confidence interval for life expectancy of a new GE light bulb. 64 bulbs are randomly selected and a mean of 750 hours and a standard deviation of 20 hours is found. Assume the distribution of life expectancy is normally distributed.

Answer 1

 Construct a 99% confidence interval for life expectancy of a new GE light bulb:

n = 64
Xbar = 750
s.d. = 20
Critical z value at 99% confidence = 2.576

margin of Error, E = 2.576*20/√64 = 6.44

99% confidence interval for life expectancy of a new GE light bulb = (Xbar - E; Xbar + E) = (743.56; 756.44)