Answer :
The conditional probability is given by:
[tex]P(A|B)=\frac{P(A\cap B)}{P(B)}[/tex]Now, since the event A is "the outcome is prime" and the event B is "the outcome is less than or equal to 2" we have that:
[tex]P(B)=0.5[/tex]and
[tex]P(A\cap B)=0.5[/tex]Therefore:
[tex]P(A|B)=\frac{0.5}{0.5}=1[/tex]Therefore the probability is 1.