Statistics homework help.
- (6) It has been suggested that the average Facebook user spends 6 hours a week on the site. If we assume a normal distribution, with a population standard deviation of 3 hours…
i.(3) What percentage of users spend more than 9 hours on Facebook?
ii.(3) What percentage of users spend between 2 and 4 hours on Facebook?
- (6) On final exams, Sarah scored 90 in Economics and Martha scored 85 in Geography. We can assume that the students’ scores within each subject are approximately “normal” in distribution. The mean scores in Economics and Geography were both 72. The standard deviation in Economics was 12 points, while in Geography it was 8.
Which of the two students has a better score, compared with his/her fellow students? Please show how you arrived at your conclusion.
- (4) What is the difference between random sampling, stratified random sampling, and cluster sampling? How might random sampling of the entire population in the US help us understand the current spread of COVID-19, rather than just testing people who show symptoms?
- A group of researchers at the University of Texas-Houston conducted a comprehensive study of pregnant cocaine-dependent women (Journal of Drug Issues, Summer 1997). All the women in the study used cocaine on a regular basis for more than a year. One of the many variables measured was birth weight (in grams) of the baby delivered. For a sample of 16 cocaine-dependent women, the mean birth weight was 2,971 grams and the standard deviation was 410 grams. Test the hypothesis that the true mean birth weight of babies delivered by cocaine-dependent women is less than 3,100 grams. Use alpha = .05.
- (3) Confidence bands for population means are smaller if you (1) know the standard deviation of the population, instead of estimating it from the sample, or (2) if you decrease the level of confidence required. In addition to these two possibilities, how else could you obtain a smaller confidence band?
- (3) We can calculate confidence bands for means by using z-values from a normal distribution table (or t-values from a t-distribution table), even if the population under study is not normally distributed. Briefly explain the property of random samples that makes this possible.