I believe it is 4/12 since you have a total of 12 marbles and only 4 are red plastic ones
A combination in this question, is combining 2 activities out of the 3.
The possible combinations are:
- Parade and Roller Coaster.
- Parade and Eat Ice Cream Cones.
- Roller Coaster and Eat Ice Cream Cones.
If you need the opposite order:
- Roller Coaster and Roller Coaster.
- Roller Coaster and Eat Ice Cream Cones.
- Eat Ice Cream Cones and Roller Coaster.
Hope This Helped! Good Luck!
The answer would be 7/4 because you would just divide both the 21 and 12 by 3