What type of sampling is this: group the students in a local college by year and then randomly select 15 students from each group

What are the coordinates of the midpoint of ab? ,1/2) /2,-1) ,-3/2) /2,-2)

If a || b and b | y, then ? a) x || y. b) x | a. c) a | y. d) a || y.

Mario has $14.35 left in his wallet. he spent $148.43 for tablecloths. then, he spent $92.05 for napkins. how much money did mario have in his wallet to start with?