Radioactive gas has been found in their lockers! The radioactive gas radon, found in some lockers, poses a health risk to students. To assess the level of contamination in the school, a county health department wants to test a few lockers. If the risk seems high, they will publicize the results to emphasize the need for more testing. Officials plan to use a list of students from the attendance office to randomly choose 25 lockers from various areas of the school.