Final answer:
a) The standard error of the mean is 2.4 days. b) The interval centered on the mean that captures 68% of the sample means is 72.6 to 77.4 days.
Step-by-step explanation:
a) The standard error of the mean can be calculated using the formula: standard error = standard deviation / square root of sample size. In this case, the standard deviation is 12 days and the sample size is 25. Therefore, the standard error of the mean is 12 / √25 = 12 / 5 = 2.4 days.
b) To find the interval centered on the mean of the sampling distribution that captures 68% of the sample means, we need to find the z-score corresponding to 68% in a standard normal distribution. The z-score can be found using a z-table or a calculator, and it is approximately 1. Therefore, the interval can be calculated as follows:
Lower limit = mean - (z-score * standard error) = 75 - (1 * 2.4) = 72.6 days
Upper limit = mean + (z-score * standard error) = 75 + (1 * 2.4) = 77.4 days