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Tutorial solutions week 13

# Tutorial solutions week 13 - BES Tutorial Sample Solutions...

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1 BES Tutorial Sample Solutions, S2/13 WEEK 13 TUTORIAL EXERCISES (To be discussed in the week starting October 28) 1. It is claimed by a manufacturer that its new type of light bulb is subject to less variability of bulb life. It is known that the former bulb type had a standard deviation of life of 150 hours. To test this claim, a consumer organization takes a sample of 41 of these new bulbs and measures their lives, finding a standard deviation of bulb life of 140 hours. Assuming light bulb lives are approximately normally distributed, test the manufacturer’s claim at a 5% level of significance. n = 41, s = 140 Under ( ) Decision rule: Reject if Since calculated we do not reject and conclude that the manufacturer’s claim of lower bulb life variability is not supported by the data. 2. Given the information of Question 1 above, calculate a 95% confidence interval for the variance of bulb life. Since n = 41 and = 0.05 we have:

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2 The confidence interval is then given by ( ( ) ( ) ) ( ) ( ) 3.
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