A company claims that their lightbulbs last an average of 400 days. To test this claim,...
A company claims that their lightbulbs last an average of 400 days. To test this claim, a random sample of 25 lightbulbs is tested and it is observed that they last for an average of 380 days with a standard deviation of 60 days.
Part A) Assuming that the population of the time to failure of all lightbulbs is normally distributed, test the null hypothesis that the average life-length of their lightbulb is 400 days against the alternative that it is less than 400 days. Use a significance level of 0.05.
Part B) Use a significance level of 0.05 to test the null
hypothesis that the population standard deviation is 80 days
against the alternative that it is not equal to 80 days.
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A company claims that their lightbulbs last an average of 400
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