9. In a time and motion study, it was found that the average time required by workers to complete a certain manual operation was 26.6 minutes with a standard deviation of 3 minutes. A group of 25...

9. In a time and motion study, it was found that the average time required by workers to complete a certain manual operation was 26.6 minutes with a standard deviation of 3 minutes. A group of 25 workers was randomly chosen to receive a special training for 2 weeks. After the training, it was found out that their average time was 24 minutes. Can it

be concluded that the special training speeds up the operation? Use a 0.05 level of significance.