Twelve auto engine crankshafts measure:
224.120; 224.001; 224.017; 223.982; 223.989; 223. 961; 223.960; 224.089; 223.987; 223.976; 223.902; 223.980.
The dimension is supposed to be 224 mm and the variance is unknown for the manufacturing process. Is there evidence that the mean dimension is not 221 mm? Assume the population is normally distributed. Use a = 0.05 and the critical value value method.