Answer: D. You are right the means of a few large samples will yield more reliable results.
Explanation: In designing a study to determine the ideal mean of cost for a discretionary service, the mean of a few large samples will yield more reliable results.
Large sample has a sample size of n greater or equal to 30, n means number of samples. Large sample size is considered important in research because large sample provide an accurate and reliable mean and small margin of error.