PSTAT 109: Lab 8 complete solutions correct answers key

PSTAT 109: Lab 8 complete solutions correct answers key

Fall 2015

Instructions: When you _nish all problems, ask your TA to check your work.

Problem 1 (Compute CI for small sample using t-distribution given sample statistics).

From a population of normally distributed IQ scores, a random sample of 25 scores yields

sample mean as _X = 98:4 and sample deviation Sx = 14:2. Find a 98% con_dence interval

for the true mean score _ of this population. Use Excel's TINV function to obtain your

answer.

Problem 2 (Compute CI using t-distribution given raw data). Standardized test scores are

often found to be normally distributed. The data set below is a random sample of combined

SAT scores from a group of sophomores picked from a random university. Compute the

sample mean, sample deviation and _nd a 95% con_dence interval for the mean SAT score

of sophomores at this university.

1270 1110 1280 970 720 1350 1070

1220 1220 1020 1210 1170 910 1320

1160 1150 880 1030 1070 1120

950 1440 1080 1020 860 980

1070 850 1200 1400 920 800

Use Excel's TINV function to obtain your answer.

Problem 3 (Compare CI using z-score and t-score). A random sample of size 400 from a

normally distributed population yields _X = 980:5 and Sx = 56:3. Compare the results of

_nding a 99% con_dence interval for _ when using z-scores rather than t-scores. Use Excel's

TINV and NORMINV functions to obtain your answer.