Work sheet #8 STA 2023

a) Find the z-score or t-score for each ( Make sure you write “z = “ or “t = “ ) Round z’s to 2 decimal places and t’s to 3 decimal places – like the tables!

b) Tell if it is unusual or not unusual.

1) The mean for all Statistics final exams is m = 75. A sample of 16 students had a mean of 77 and s = 15.

2) The mean for this class of 28 students is 75 and s = 14. One student got a 70.

3) The mean SAT score for those who took it in 2002 was 1023 and s = 209. The average for a sample of 25 students was 1117.

4) The mean SAT score for a sample of 15 students who took the SAT in April 2002 was 1042 and s = 212. One student got a score of 1220.

5) A sample of 80 students found the mean time to complete a 4-year degree was 5.15 years with s = 1.68 compared to the population mean of 5 years.

6) A sample of 20 students found that the mean time they spent doing their Stats homework each week was 5.6 hours with s = 1.3 hours. The population mean from last year was 5.9 hours.

7)10% of the general population are left-handed. A survey of 200 carpenters found 27 who are left-handed.

8) Chickens are normally distributed with a mean weight of 62.2 . In an experiment with a new enriched feed mixture, nine chickens weighed the following:

61.4 62.2 66.9 63.3 66.2 66.0 63.1 63.7 66.5

9) The mean time for the 100-meter dash for men in the last 2 summer Olympic games was 10.5 seconds. The following is a sample from the last major competition:

12.01 11.07 11.03 11.24 10.86 10.83 10.61 10.82 10.35 10.36 10.32

10.45 10.53 10.23 9.95 10.14 10.06 10.25 9.99 9.92 9.96

10) The mean amount of active ingredient in a cold medicine is supposed to be 600 mg. A sample of 40 doses found the mean to be 593 with s = 21.