Statistics-PSTAT 109: Lab 8 Fall 2015 Instructions

PSTAT 109: Lab 8Fall 2015Instructions: When you finish 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% confidence intervalfor the true mean score µ of this population. Use Excel’s TINV function to obtain youranswer.Problem 2 (Compute CI using t-distribution given raw data). Standardized test scores areoften found to be normally distributed. The data set below is a random sample of combinedSAT scores from a group of sophomores picked from a random university. Compute thesample mean, sample deviation and find a 95% confidence interval for the mean SAT scoreof sophomores at this university.127012201160950107011101220115014408501280102088010801200970 720 1350 10701210 1170 910 13201030 1070 11201020 860 9801400 920 800Use 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 offinding a 99% confidence interval for µ when using z-scores rather than t-scores. Use Excel’sTINV and NORMINV functions to obtain your answer.

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