NO LINKS OR ANSWERING QUESTIONS YOU DON'T KNOW. Use the following information for problems 19-21​

12 red + 16 blue + 18 white = 46 marbles

9. 3 marbles NO replacement: no white?
28/46 x 27/45 x 26/44
0.61 x 0.6 x 0.59 is about 22%

Each time we pick a red or blue we have one less to choose from next time

10. 4 marbles WITH replacement: all white?
18/46 x 18/46 x 18/46 x 18/46
0.39 x 0.39 x 0.39 x 0.39 is about 2%

11. 2 marbles NO replacement: red then blue

12/46 x 16/45
12 x 45 / 16 x 46
540/736
135/184 :)