In an examination of purchasing patterns of shoppers, a sample of 16 shoppers revealed that they spent, on average, $54 per hour of shopping. Based on previous years, the population standard deviation is thought to be $21 per hour of shopping. Assuming that the amount spent per hour of shopping is normally distributed, find a 90% confidence interval for the mean amount.
- [$51.8409, $56.1591]
- [$52.3174, $55.6826]
- [$45.3637, $62.6363]
- [$47.2695, $60.7305]