We will assume that the 8-sided die has the numbers :
1 2 3 4 5 6 7 8
The prime numbers are : 2 3 5 7
Then the outcomes are 2 3 5 7
The probability of having a prime number if the die rolled once= 4/8=1/2.
Math
We will assume that the 8-sided die has the numbers :
1 2 3 4 5 6 7 8
The prime numbers are : 2 3 5 7
Then the outcomes are 2 3 5 7
The probability of having a prime number if the die rolled once= 4/8=1/2.