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Confidence Interval

1. The following sample of 16 measurements was selected from a population that is approximately normally distributed: 91 80 99 110 95 106 78 121 106 10 97 82 100 83 115 104. Construct a 95% confidence interval for the population mean.

2. In a survey of 1000 persons, 290 responded that they approve of the president's job performance. Find the 95% confidence interval for the true population proportion.

3. A manufacturer of official NFL footballs uses a machine to calibrate the new balls to a pressure of 13.5 lbs. When the machine is calibrated the mean inflation pressure is 13.5 lbs, but uncontrollable factors cause the individual pressures to vary randomly from 13.3 to 13.7 lbs. For quality control purposes, the manufacturer wished to estimate the mean inflation pressure to within 0.025 lbs of its true value with a 99% confidence interval. What is the minimum sample size needed? To estimate the population standard deviation, use the formula s=range of observations / 4.

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