Twelve bank tellers were randomly sampled and it was determined that they made an average error of 3.6 errors per day with a sample standard deviation of 0.42 error. Construct a 90 percent confidence...

Twelve bank tellers were randomly sampled and it was determined that they made an average error of 3.6 errors per day with a sample standard deviation of 0.42 error. Construct a 90 percent confidence interval for the population mean of errors per day. What assumption is implied about the number of errors bank tellers make?