Question

A study of the ages of motorcyclists killed in crashes involves the random selection of 132

drivers with a sample mean of 32.95 years. Assume that the SAMPLE standard deviation is 9.4 years. a) Find the critical value tα /2 for a 90% confidence interval

b) Construct and interpret the 90% confidence interval estimate of the mean age of all motorcyclists killed in crashes. Use the z-table method.

dence interval.

Question 2. Randomly selected statistics students of the author participated in an experiment to test their ability to determine when 60 seconds has passed. Forty students yielded a sample mean of

57.3 sec. Assume that the sample standard deviation is σ = 8.5 sec.

1. a) Find the critical value tα /2 for a 80% confidence interval

2. b) Construct a 80% confidence interval estimate of the population mean of all statistics students. Use the z-table method.

3. c) Use TI84/83 calculator method.

4. d) Write a conclusion.

Answer 1

1) a) t critical value = 1.657 at n = 132 and alpha = 0.10

b) 90% Confidece interval :

The 90% confidence that the true mean age of all motorcyclists killed in crashes is lies between 31.595 and 34.305

2) a) Critical value Z alpha /2 = 1.282 at 80% confidece coefficeint

b)

c) TI-83 Procedure:

Press [STAT]->Stats>7. Z-interval [ENTER]

Move curson to Stats

Enter the data as follows

Enter on Calculate, the output be

d) The 80% confidence the true (population) mean of all statistics students is lies between 55.578 and 59.022