The plant manager at an aluminium processing plant in KZN recorded the percentage of scrap produced daily by a sheet rolling machine. Scrap is measured as a percentage of daily machine output.
(a) Use the Histogram option from Data Analysis to examine whether the daily percentage scrap from the machine is normally distributed. Comment on the findings.
(b) Use the Descriptive Statistics option from Data Analysis to derive the 95% confidence interval estimate for the actual mean percentage of scrap produced daily by the machine. Interpret the findings.
(c) It is company policy that a machine must be stopped and fully serviced if its average daily percentage scrap is 3.75% or more. Test, at the 5% significance level, whether the machine is due for a full service. Use the TINV function to find the critical test statistic. Use the findings from (b) to compute t-stat.