The sample space is {1,2,3,4,5,6}

A.  The only perfect squares in the sample space are 1 and 4.
    That's because 1 = 1² and 4 = 2².

That's 2 ways out of 6 ways that a perfect square number can
be rolled.  "Out of" means "over", so the probability is
2 over 6 or 2/6 and that reduces to 1/3.

B.  The only prime numbers in the sample space are 2,3 and 5.
    
That's 3 ways out of 6 ways that a prime number can be
be rolled.  "Out of" means "over", so the probability is
3 over 6 or 3/6 and that reduces to 1/2.


Edwin