The labor relations manager of large corporation wished to study the absenteeism among workers at company's central office throughout the last year. A random sample of 25 workers revealed following: an average of 9.7 days; a standard deviation of 4.0 days; and 12 employees were absent more than 10 days. In determining a 95% confidence interval estimate of average number of days absent for the company's workers last year what will be the standard error?