STAT 212PROBLEM SET 2.pdf - EGERTON UNIVERSITY STAT 212 PRINCIPLES OF STATISTICAL INFERENCE PROBLEM SET 2 1 The life in hours of a 75-watt light bulb is

# STAT 212PROBLEM SET 2.pdf - EGERTON UNIVERSITY STAT 212...

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EGERTON UNIVERSITY STAT 212: PRINCIPLES OF STATISTICAL INFERENCE PROBLEM SET 2 1. The life in hours of a 75-watt light bulb is known to be normally distributed with 25 hours. A random sample of 20 bulbs has a mean life of hours. Construct a 95% confidence interval on the mean life. 2. The yield of a chemical process is being studied. From previous experience yield is known to be normally distributed and 3 . The past five days of plant operation have resulted in the following percent yields: 91.6, 88.75, 90.8, 89.95, and 91.3. Find a 95% two-sided confidence interval on the true mean yield. 3. In a study regarding the length of time students required to earn a bachelors degree, 80 students are randomly selected and are found to have a mean of 4.8 years. Assuming σ is known to be 2.2 years, construct a 95% confidence interval estimate of the population mean. 4. When people smoke, the nicotine they absorb is converted to cotinine (coat-in-ene), which can be measured. A sample of 40 smokers has a mean cotinine level of 172.5. Assuming that σ is known to be 119.5, find a 90% confidence interval estimate of the mean cotinine level of all smokers. 5. In measuring reaction time, a psychologist estimates that the standard deviation is 0.05 seconds. How large a sample of measurements must he take in order to be 99% confident that the error of his estimate will not exceed 0.01 second?

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