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Chapter 13 13.1 (a) Counts will be obtained from the samples so this is a problem about comparing proportions. (b) This is an observational study comparing random samples selected from two independent populations. 13.2 (a) Scores will be obtained from the samples so this is a problem about comparing means (average scores). (b) This is an experiment because the researchers an imposing a “treatment” and measuring a response variable. Since these are volunteers we will not be able to generalize the results to all gamers. 13.3 (a) Two samples. The two segments are used by two independent groups of children. (b) Paired data. The two segments are both used by each child. 13.4 (a) Single sample. The sample mean will be compared with the known concentration. (b) Two samples. The mean concentration in 10 beakers with the new method will be compared to the mean concentration in 10 different beakers with the old method 13.5 (a) 0:THCµµ=versus :aTCHµµ>, where Tµand Cµare the mean improvement of reading ability of the treatment and control group respectively. (b) The treatment group is slightly left-skewed with a greater mean and smaller standard deviation (x=51.48, s=11.01) than the control group (x=41.52, s=17.15). The histograms below show no serious departures from Normality for the treatment group (on the left) and one unusually large score for the control group (on the right). DRP score (treatment group)Count80604020543210DRP score (control group)Count8060402076543210The boxplot (on the left below) also shows that the median DRP score is higher for the treatment group and the IQR is higher for the control group. Notice that the unusually high score is not identified as an outlier by Minitab. The combined Normal probability plot (on the right below) shows an overall liner trend for both sets of scores, so the Normal condition is satisfied for both groups. 274Chapter 13