What is obtained by dividing the population into groups and selecting all individuals from within a random sample of the groups ?

Which expression is equivalent to (3^2)^-2 a.-81 b.-12 c.1/81 d.1/12

What is the ratio for the surface areas of the cones shown below, given that they are similar and that the ratio of their radil and altitudes is 4: 3? 23

In a singing competition, there are 150 participants. at the end of each round, 40% of the participants are eliminated. how many participants are left after n rounds?