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.425

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  1. 1. In the Chicago area, the price of new tires is normally distributed with a standard deviation of  = $11.50. A random sample of 64 tires indicates a mean selling price of x = $98.70. Construct an 85% confidence interval for the mean selling price, µ of this new tire in the Chicago area. In order to estimate within $10.00 of the population mean, how large of a sample should be taken in order to be 95% confident of achieving this level of accuracy. .425 -1.44 1.44

  2. 2.Fifty electric bills from the apartment of a certain city apartment are chosen at random. The mean electric bill was x = $109.50 with s = $21.75. The electric bills have a normal distribution. Construct a 98% confidence interval for P. .49 -2.33 2.33

  3. 3.Thirty SAT scores were chosen at random from the records of seniors at a certain high school over the last 20 years. 770 680 510 520 660 680 660 500 570 680 800 660 560 690 700 720 800 420 • 620 660 800 420 380 740 770 680 • 500 660 Construct a 95% confidence interval for the population mean µ. .475 -1.96 1.96

  4. A random sample on n = 100 voters in a community produced x = 59 voters in favor of a candidate A. Estimate the fraction of the voting population favoring candidate A using a 95% and a 90% confidence interval.

  5. How many people must be asked if candidate A wants A 95% confidence interval with a margin of error of + 3 %?

  6. A recent poll cited that 76 out of 180 randomly chosen Households watch at least 2 hours of public television per week. Find a 90% confidence interval for p, the proportion of households that watch at least 2 hours of public television per week.

  7. How many people must be asked if the station wants a 90% confidence interval with a margin of error of + 4 %?

  8. A manufacturer of gunpowder claims to have developed a gun powder that is designed to produce a muzzle velocity of 3000 ft sec. The following data is collected in ft/sec 3005 2925 2935 2965 2995 3005 2935 2905. Construct a 95% and a 85% confidence interval for µ.

  9. The profit for a car dealership for the past week was $210 $300 $120 $620 $450 $510 Construct a 90% confidence interval for the average pofit

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