Aprofessor must randomly select 4 students to participate in a mock debate. there are 20 students in his class. in how many different ways can these students be selected, if the order of selection does not matter?

Any is very appreciated! (picture is provided below)not sure how to do this at all won't lie

17. a researcher measures three variables, x, y, and z for each individual in a sample of n = 20. the pearson correlations for this sample are rxy = 0.6, rxz = 0.4, and ryz = 0.7. a. find the partial correlation between x and y, holding z constant. b. find the partial correlation between x and z, holding y constant. (hint: simply switch the labels for the variables y and z to correspond with the labels in the equation.) gravetter, frederick j. statistics for the behavioral sciences (p. 526). cengage learning. kindle edition.

Kayaks rent for $35 per day. which expression can you use to find the cost in dollars of renting 3 kayaks for a day?