This Problem Set is a part of the Lesson 23, Unit 5, Grade 7. Students use data from random samples to draw informal inferences about the difference in population means. The bottom line is that if two sample means are separated by at least 2 MADs, then it is reasonable to conclude that there is a difference between the two corresponding population means. Recall that in Lesson 21, a difference between two sample means was called meaningful if it is greater than what would have been expected just due to sampling variability.