SOLUTION: A bag contains a red marble, a blue marble and a yellow marble. A marble is selected at random 3 times with replacement. How many events will form a full group of events? Also,

There are 3 ways to draw the first marble.
For each of these 3 ways to draw the first marble,
there are 3 ways to draw the second marble.
That's 3×3 or 9 ways to draw the first two marbles.
For each of these 9 ways to draw the first two marbles,
there are 3 ways to draw the third marble.
That's 9×3 or 27 ways to draw all three marbles.

Here they are listed two ways:

You can list them with a tree diagram like this: 
 


                                     R = RRR
                                    /
                                   R-B = RRB
                                  / \
                                 /   Y = RRY
                                /
                               /     R = RBR
                              /     /
                             R-----B-B = RBB
                            / \     \
                           /   \     Y = RBY
                          /     \
                         /       \   R = RYR
                        /         \ /
                       /           Y-B = RYB
                      /             \
                     /               Y = RYY
                    /
                   /                 R = BRR
                  /                 /
                 /                 R-B = BRB
                /                 / \
               /                 /   Y = BRY
              /                 /
             /                 /     R = BBR
            /                 /     /
     START /-----------------B-----B-B = BBB
            \                 \     \
             \                 \     Y = BBY
              \                 \
               \                 \   R = BYR
                \                 \ /
                 \                 Y-B = BYB
                  \                 \
                   \                 Y = BYY
                    \
                     \               R = YRR
                      \             /
                       \           R-B = YRB
                        \         / \
                         \       /   Y = YRY
                          \     /
                           \   /     R = YBR
                            \ /     /
                             Y-----B-B = YBB
                              \     \
                               \     Y = YBY
                                \
                                 \   R = YYR
                                  \ /
                                   Y-B = YYB
                                    \
                                     Y = YYY

Or you can just list them all like this:

 1. Red first, Red second, Red third
 2. Red first, Red second, Blue third
 3. Red first, Red second, Yellow third
 4. Red first, Blue second, Red third
 5. Red first, Blue second, Blue third
 6. Red first, Blue second, Yellow third
 7. Red first, Yellow second, Red third
 8. Red first, Yellow second, Blue third
 9. Red first, Yellow second, Yellow third
10. Blue first, Red second, Red third
11. Blue first, Red second, Blue third
12. Blue first, Red second, Yellow third
13. Blue first, Blue second, Red third
14. Blue first, Blue second, Blue third
15. Blue first, Blue second, Yellow third
16. Blue first, Yellow second, Red third
17. Blue first, Yellow second, Blue third
18. Blue first, Yellow second, Yellow third
19. Yellow first, Red second, Red third
20. Yellow first, Red second, Blue third
21. Yellow first, Red second, Yellow third
22. Yellow first, Blue second, Red third
23. Yellow first, Blue second, Blue third
24. Yellow first, Blue second, Yellow third
25. Yellow first, Yellow second, Red third
26. Yellow first, Yellow second, Blue third
27. Yellow first, Yellow second, Yellow third

Edwin