Final answer:
The sample mean is 0.372 and the margin of error is 0.068.
Step-by-step explanation:
To find the margin of error and the sample mean using the given confidence interval (0.304, 0.440), we need to find the midpoint of the interval.
The midpoint is calculated by taking the average of the lower bound and the upper bound: (0.304 + 0.440) / 2 = 0.372.
Therefore, the sample mean is 0.372 and the margin of error is half the length of the interval, which is (0.440 - 0.304) / 2 = 0.068.