A band director is trying to decide what music to play for the halftime show. To get a sample, the director divides the band into groups based on their grade (freshmen, sophomores, juniors, and seniors). Then she randomly chooses a group and surveys every member of the chosen group. Which sampling method was used? cluster sampling
simple random sampling
stratified random sampling
systematic random sampling helo​

Ascientist has 50 grams of a radioactive element. the amount of radioactive element remaining after t days can be determined using the equation (1) after two days the scientist receives a second shipment of 50 grams of the same element. the equation used to represent the amount of shipment 2 remaining after t days is 10) - 50 which of the following is an equivalent form of the expression for the amount remaining in shipment 2? what’s the answer?