1. If z is a standard normal variable, find the probability that z is less than 1.13
a. 0.1292
b. 0.8708
c. 0.8485
d. 0.8907
2. Suppose that X has a normal distribution. Find the indicated probability. The mean is 15.2 and the standard deviation is 0.9. Find the probability that X is greater than 17.
a. 0.9713
b. 0.9821
c. 0.0228
d. 0.9772
3. Use the confidence level and the example data to find a confidence interval for the estimation of the mu population. Round your answer to the same number of decimal places as the sample mean. A random sample of 105 light bulbs had a half-life of 441 hours with a standard deviation of 40 hours. Build a 90% confidence interval for the half-life, mu, of all light bulbs of this type.
a. 433 hr
b. 435 hr
c. 431 hr
d. 432 hr
4. Resolve the problem. The weights of the fish in a given lake are distributed normally with an average of 19 pounds and a standard deviation of 6. If 4 fish are selected at random, what is the probability that the average weight is between 16.6 and 22.6 pounds?
a. 0.0968
b. 0.4032
c. .6730
d. 0.3270
5. Use the information given to find the minimum sample size required to estimate an unknown population mean mu. How many women should be selected at random to estimate the average weight of women in the age group. We want the 90% confidence that the sample mean is within 3.7 pounds of the population mean and the standard deviation of the population is known to be £ 28
a. 221
b. 156
c. 153
d. 155
6. Use the confidence level and data in the example to find the margin of error E. Round your answer to the same number of decimal places as the sample mean unless otherwise indicated. Annual earnings of university students, confidence: 99%, n = 76 = $ 3016, σ = $ 872
a. $ 196
b. $ 891
c. $ 233
d. $ 258
7. Use the confidence level and the sample data given to construct a confidence interval for the population proportion p. n = 110, x = 55; 88% confidence
a. 0.425
b. 0.421
c. 0.422
d. 0.426
8. Assume that a sample is used to estimate a mu population mean. Use the confidence level and sample data to find the margin of error. Assume that the sample is a simple random sample and the population has a normal distribution. Round your answer to one decimal more than the standard deviation of the sample. 95% confidence, n = 21; sigma = 0.16
a. 0.085
b. 0.068
c. 0.063
d. 0.073