If the probability of the event A is P(A) and the probability of the event B is P(B), then the probability P(A and B) is P(A)*P(B).
Since both P(A) and P(B) are equal to 1/2, then:
[tex]P(A\text{ and }B)=P(A)\cdot P(B)=\frac{1}{2}\cdot\frac{1}{2}=\frac{1}{4}[/tex]