12. A team of psychologists compared college students’ ability to concentrate under different noise conditions: constant background noise, unpredictable noise, and no noise.

Psychologists randomly selected 30 participants and randomly split them into three groups. The ability to concentrate was measured by a speed test that consists of a large number of easy questions. The speed test scores are normally distributed. Higher scores mean better concentration. The speed test scores from each group were reported in Table 12.11.