# Stats Assignment Questions

August 30, 2017

Question
1. find za/2 for a= 0.09

2. the mean and standard deviation of a random sample of n measurements are equal to 33.5 and 3.8, respectively.

a. find a 90% confidence interval for u if n=64

b.find a 90% confidence interval for u if n= 256

c.find the widths of the confidence intervals found in parts a and b. what is the effect on the width of a confidence interval of quadrupling the sample size while holding the confidence coefficient fixed?

3.based on a sample of 1160 adults, the mean amount of sleep per night is 7.81 hours. Assuming the population standard deviation for mount of sleep per night is 2.8 hrs, construct and interpret a 90% confidence interval for the mean amount of sleep per night.

a random sample of 1050 satellite radio subscribers were asked, “do you have a satellite radio receiver in your car?”. The survey found that 210 subscribers did, in fact, have a satellite reciever in there car.
a. From the sample, calculate an estimate of true proportion of satellite radio subscribers who have a satellite radio receiver in their car

b. Form a 99% confidence interval or the estimate, part a

c. Give an interpretation of the interval, part b

If you wish to estimate population mean with a sampling distribution error SE=0.28 using a 95% confidence interval and you know from prior sampling that o^2 is approximately equal to 3.3 how many observations would have to be included in your sample?

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