The ages of pennies at a particular bank follow a nearly normal distribution with mean 10.44 years with standard deviation 9.2 years. Say you take random samples of 30 pennies, find the mean age in each sample, and plot the distribution of these means. Which of the following are the best estimates for the center and spread of this distribution? a. mean = 10.44, standard error = 9.2
b. mean = 10.44, standard error = 9.2/30 = 0.31
c. mean = 10.44/30 = 0.348, standard error = (9.2/30)2 = 0.094
d. mean = 10.44, standard error = 9.2/30 = 1.68