The parent-teacher association wants to find out how much students pay for school supplies at the beginning of the school year, so it conducts a survey at certain local stores. PTA members visit these stores to find the prices of the items on the students' supply list. What is the sample in this study?

The weight of a radioactive isotope was 96 grams at the start of an experiment. after one hour, the weight of the isotope was half of its initial weight. after two hours, the weight of the isotope was half of its weight the previous hour. if this pattern continues, which of the following graphs represents the weight of the radioactive isotope over time? a. graph w b. graph x c. graph y d. graph z