2. A light-bulb manufacturer regularly advertises that his bulbs last 900 hours with a standard deviation of 75 hours. A random sample is chosen before each campaign to make sure that the claim is correct. If one such sample of 20 bulbs show a mean of 925 hours, can the advertising claim be considered an underestimate at the 0.05 level of significance? Find t statist to acce 3. A psychologist believes that it will take at least an hour for certain disturbed Hypo children to learn a task. A random sample of 30 of these children results in a mean of 50 minutes to learn the task. Should the psychologist modify her belief Ho: H at the 0.01 level if the population standard deviation can be assumed to be 15 Ha: minutes? 15 Ho:H = 80 X = 75 Hail