Final answer:
The simplified ratio of the total number of students in the class to the number of students dressed as witches is 8:3, assuming the class consists only of the students mentioned.
Step-by-step explanation:
The question asks for the ratio of the entire class to the number of students dressed as witches for Halloween. To find this, we need to know the total number of students in the class. Assuming that the class only consists of the zombies and witches, we add the number of students dressed as zombies (20) to the number of students dressed as witches (12). This gives us a class total of 32 students.
Now, we calculate the ratio of the entire class to students dressed as witches. The entire class has 32 students and there are 12 witches, thus the ratio is 32:12. To simplify, we can divide both numbers by the greatest common divisor, which is 4, resulting in a ratio of 8:3.
To express the ratio in simplest form, it is 8:3, meaning for every 8 students in the class, there are 3 students dressed as witches.