Many couples believe that it is getting too expensive to host an "average" wedding in the United States. According to a statistics study in the U.S., the average cost of a wedding in the U.S. in 2014 was $25,200. Recently, in a random sample of 35 weddings in the U.S. it was found that the average cost of a wedding was $24,224 with a standard deviation of $2,210.
For this description, which of the following does NOT describe a required condition for a valid confidence interval based on the sample results?
a. The sample distribution must be normally distributed in order to have a valid confidence interval. The problem does not describe the distribution of the sample, so this condition is not met.
b. The sample observations are independent because knowledge about the cost of any one wedding tells us nothing about the cost of any other wedding in the sample.
c. The description states that the sample was randomly selected, so we can assume that the condition which states that the data must represent a random sample is satisfied.
d. The sample size of 35 is large enough that knowledge about the population distribution is not necessary and the condition that the population be normally distributed or sample size be larger than 30 is satisfied.