The life in hours of a 75-watt light bulb is known to be normally distributed with standard deviation σ = 25 hours. A random sample of 20 bulbs results in a mean life of 1014 hours. Determine the following: (a) Construct a 95% two-sided CI on the mean life. (b) Construct a 95% lower confidence bound on the mean life.

a) (1008.34,1019.658) b) (1009.24,1018.76)

Step-by-step explanation:

Since we have given that

n = 75

mean = 1014 hours

Standard deviation = 25 hours

At 95% two sided , z = 1.96

So, confidence interval would be

(b) Construct a 95% lower confidence bound on the mean life.

z = 1.65

So, confidence interval would be

Hence, a) (1008.34,1019.658) b) (1009.24,1018.76)