Question

The lifetime of 225 light bulbs is measured and the sample mean and sample variance are found to be 223 hr and 100 hr2 , respectively. (a) Find a 95% confidence interval for the mean lifetime. (b) Find a 95% confidence interval for the variance of the lifetime.

Answer 1

Sample mean=223hr

Sample variance=100hr²

a)

For 95%

223-2.92$\le$ 223$\le$ 223+5.62

220.08$\le$ 223$\le$ 228.62

b)

For 95%

87.3$\le$ 100$\le$ 112.7