Weight of a rock: In a geology course, students are learning to use a balance scale to accurately weigh rocks. One student plans to weigh a rock 20 times and then calculate the average of the 20 measurements to estimate her rock's true weight. A second student plans to weigh a rock 5 times and calculate the average of the 5 measurements to estimate his rock's true weight. The student who weighs his rock 5 times uses the mean to calculate the 95% confidence interval for the rock weight (in grams). His interval is (25.2, 29.1). What does a 95% confidence interval for rock weight tell us in this case? We are 95% confident that this interval includes the mean of the 5 weight measurements taken by this student. We are 95% confident that most rocks of this type weigh between 25.2 g and 29.1 g. We are 95% confident that the true weight of the rock is between 25.2 g and 29.1 g