Question

a light bulb manufacturer guarantees that the mean life of a certain type of light bulb is at least 762 hours.A random sample of 20 light bulbs has a mean life of 736 hours. assume the population. is normally distributed and the population standard deviation is 65 hours. at a=0.08

Answer 1

Significance level :

Test statistic :

This is a left tailed test

critical value : ( using excel formula NORM.S.INV(0.08) )

Rejection region : T < -1.4051

P-value = 0.0368 ( using excel formula NORM.S.DIST(-1.7889,TRUE))

Since the P value is less than the significance level 0.08, and test statistic lie in the rejection region we shall reject the null hypothesis.

Thus we have evidence to reject the claim of the light bulb manufacturer that guarantees that the mean life of a certain type of light bulb is at least 762 hours.