Question

An electrical firm manufactures light bulbs that have a lifetime that is approximately normally distributed with a mean of 800 hours and a standard deviation of 40 hours. Test the claim, at the 0.05 level of significance, if a random sample of 30 bulbs has an average life of 790 hours. Also, Find P-value

Answer 1

This is the two tailed test .

The null and alternative hypothesis is

H₀ : = 800

H_a : 800

Test statistic = z

= ( - ) / / n

= (790 - 800) / 40 / 30

Test statistic = 1.37

P-value = 0.1707

= 0.05

P-value >

Fail to reject the null hypothesis .