The telecommunications manager at the Lowell Call Center is concerned about the difference in average system downtime between day and night operations at the center. A random sample of 45 day shift records and 45 night shift records are examined. Average downtime for the day shift sample is 53 minutes, with a standard deviation of 18 minutes. Average downtime for the night shift sample is 48 minutes, with a standard deviation of 14 minutes. Is the difference in sample average downtimes statistically significant at the 5% significance level? Explain.