Kari plans to sample 20 people of a population that contains 100 students. she wants to determine how many people wake up before 6 a. m. which sample is the most random?
the first 20 students who arrive at school in the morning
all 20 boys on the swim team
5 students out of each of the 4 homeroom classes
the last 20 people in line for breakfast in the cafeteria

Ariana starts with 100 milligrams of a radioactive substance. the amount of the substance decreases by 20% each week for a number of weeks, w. the expression 100(1−0.2)w finds the amount of radioactive substance remaining after w weeks. which statement about this expression is true? a) it is the difference between the initial amount and the percent decrease. b) it is the difference between the initial amount and the decay factor after w weeks. c) it is the initial amount raised to the decay factor after w weeks. d) it is the product of the initial amount and the decay factor after w weeks.