Basic grading function

Let's suppose that we want to ask the question "Give a prime number". For this, we need to use a grading function.

First, let's create the grading function. This is done in the Define random variables and functions section. In this example, the grading function will be called gf. 

The function we've defined, gf(x), returns true if x is prime and false otherwise. Select Custom grading function in the Validation options section to use this as the validation method. Then, use the name of the grading function in the blank, in this case, "gf".
Caution
As you may notice, you can also define how the student's answer will be passed to the grading function. This is an advanced feature for which you can find more details in the two latest sections of this documentation page. Most user cases will require leaving the default value: Evaluated.

As for the Correct answer blank, anything will work. Since we've selected Custom grading function as the validation method, the output of the grading function is the only thing that determines correct answers. In this case, we could input a prime number, for example.