Practice

– 8.17

8.17

• 110 or greater

• Z = 105-100/3 = 1.67 p = .0475

• 90 or less

• Z = 90-100/3 = -3.33p = .0004

Practice

• For an SAT test = 500 = 100

• What is the probability that a sample of 65 people will have a mean SAT score below 525?

Step 1: Sketch out question

-3 -2 -1 0 1 2 3

Step 2: Calculate the Standard Error100 / 65 = 12.40

-3 -2 -1 0 1 2 3

Step 3: Calculate the Z score(525 - 500) / 12.40 = 2.02

-3 -2 -1 0 1 2 3

Step 4: Look up Z score in TableZ = 2.02; Column B =.4783

-3 -2 -1 0 1 2 3

.50 .4783

Practice

• There is a .9783 probability that a sample of 65 people would have a mean SAT under 525

Practice

• In a large corporation, the mean salary for all males with 3 to 5 years of experience was $28,000. Salaries (expressed in thousands) for a random sample of 10 women also having 3 to 5 years of experience were:

• 24, 27, 31, 21, 19, 26, 30, 22, 15, 36

• Construct the 95% confidence interval for women and interpret what this means relative to the mean salary of males.

Practice

• M = 25.1

• SE = 1.97

• t(9) = 2.262

• 20.64 to 29.56

• 20,640 to 29,560

Practice

8.30

0

2

4

6

8

10

12

14

16

18

T1 T2 T3 T4

Practice

• SE = 1.0

• t = 2.064

• T1 = 5.936 to 10.064

• T2 = 3.936 to 8.064

• T3 = 11.936 to 16.064

• T4 = 13.936 to 18.064

0246810

1214161820

T1 T2 T3 T4

Practice

8.23

Practice

• M= 27• S hat = 3.803• SE = 1.016• t (13)= 2.160

• LL = 24.8• UL = 29.2

• The workshop is working. We are 95% confident the average score of everyone who takes the workshop would be above 24 (the norm of the test)

Practice

– 8.12– 8.13

N 1 2 4 8

1 1 2 4 8

4 .5 1 2 4

16 .25 .5 1 2

64 .125 .25 .5 1

As N (sample size) increases the standard error decreases!

Practice Handout

Cookbook

• Bring your cookbook to class on Monday!