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.

Let’s say that the student who collected 20 weight measurements came up with a mean weight of 27.1 g with a standard deviation of 2.3 grams. The critical T-value for a 95% (one-sample) confidence interval with df = 19 is 2.09.

Which of the following is the resulting 95% confidence interval?

(25.0, 29.2)
(26.0, 28.2)
(26.6, 27.6)