A random sample of 57 children with working mothers showed that they were absent from school an average of 5.3 days per term with a standard deviation of 1.8 days. If days absent follows a normal distribution, determine the critical value for the test statistic (z or t) needed to build a 98% confidence interval for the average number of days absent per term for all children. State the positive value only exactly as found in the table (3 decimal places).
Sleep apnoea is a sleep disorder that causes a person to stop breathing momentarily and then awaken briefly. A study of 645 Victorian commercial truck drivers found that 84 of them suffered from sleep apnoea. Use the survey results to estimate, with 90% confidence, the proportion of Victorian commercial truck drivers who suffer from this sleeping disorder. Report the upper bound of the interval only, giving your answer as a percentage to two decimal places.