Final answer:
The true statement is that the sample standard deviation is unknown. While the provided confidence interval suggests the population mean is likely within 325 to 375, neither the exact population mean nor the sample mean is definitively determined by this interval.
Step-by-step explanation:
The subject of the question is Mathematics, and the specific area within mathematics is statistics and confidence intervals. A 95% confidence interval for the mean amount is provided as being 325 to 375 based on a sample of 60. When interpreting this confidence interval, it's important to understand that while we can be 95% confident that the population mean falls within this range, the interval does not guarantee this. Therefore, the true statement based on the provided information is d) The sample standard deviation is unknown.
It is incorrect to claim that the population mean could not be 377 (a), as there is still a 5% chance that the true mean falls outside the interval. Likewise, it's incorrect to assert that the population mean is definitively between 325 and 375 (b), because that's not how confidence intervals work; they provide a range of likely values, not certainties. The claim that the sample mean is exactly 350 (c) is not supported by the information given. The value of 350 is simply the midpoint of the confidence interval and does not necessarily equal the sample mean.