Susan sound predicts that students will learn most effectively with a constant background sound, as opposed to an unpredictable sound or no sound at all. she randomly divides twenty-four students into three groups of eight. all students study a passage of text for 30 minutes. those in group 1 study with background sound at a constant volume in the background. those in group 2 study with noise that changes volume periodically. those in group 3 study with no sound at all. after studying, all students take a 10 point multiple choice test over the material. does sound have any effect on the mean test scores of students?