A random sample of 64 automobiles traveling on a section of an interstate showed an average speed of 65 mph. The distribution of speeds of all cars on this section of highway is normally distributed, with a standard deviation of 13.5 mph. The 86.5% confidence interval for μ, in mph, is _ a. 63.139 to 66.861     b. 62.478 to 67.522     c. 51.500 to 78.500     d. 45 to 85

a group of 59 randomly selected students have a mean score of 29.5 with a standard deviation of 5.2 on a placement test. what is the 90% confidence interval for the mean score, u, of all students taking the test?

claim the standard deviation of pulse rates in adult women is at least 50. for a random sample of adult females the pulse rates have a standard deviation of 11.6.

The manager of a fleet of automobiles is testing two brands of radial tires and assigns one tire of each brand at random to the two rear wheels of eight cars and runs the cars until the tires wear out. The data (in kilometers) follow. Find a 99% confidence interval on the difference in the mean life. Car Brand 1 Brand 2 1 36,925 34,318 2 45,300 42,280 3 36,256 35.548 4 32,100 31,950 5 37,210 38,015 6 48,360 47,800 7 38.200 37,810 8 33,500 33,215 Round your answer to 2 decimal places. Do not use commas.

In a school district, all sixth grade students take the same standardized test. The superintendant of the school district takes a random sample of 3030 scores from all of the students who took the test. She sees that the mean score is 169169 with a standard deviation of 7.06747.0674. The superintendant wants to know if the standard deviation has changed this year. Previously, the population standard deviation was 1313. Is there evidence that the standard deviation of test scores has decreased at the α=0.005α=0.005 level? Assume the population is normally distributed. Step 1 of 5:  State the null and alternative hypotheses. Round to four decimal places when necessary. Step 2 of 5:  Determine the critical value(s) of the test statistic. If the test is two-tailed, separate the values with a comma. Round your answer to three decimal places.     Step 3 of 5:  Determine the value of the test statistic. Round your answer to three decimal places. Step 4 of 5:  Make the…

Scores on a standarized exam are known to follow a normal distribution with a standard deviation of 5. A researcher finds a random sample of 25 exam scores has a mean score of 72. Use this to find a 88% confidence interval for the mean exam score of all students taking the exam.

The mean SAT verbal score is 485​, with a standard deviation of 97. Use the empirical rule to determine what percent of the scores lie between 485 and 679. ​(Assume the data set has a​ bell-shaped distribution.)