Definition 1: Number of symmetric ways

If an event A can happen in $w_A$ ways out of a total of $w$ equally likely possible ways, then the probability of A is given by $\Pr(A)=w_A/w$. For example, the probability of getting an odd number when throwing a 6-sided die is given by $3/6$ since there are 3 ways to get an odd number (i.e. numbers {1,3,5}) out of a total of 6 equally likely outcomes (i.e. numbers {1,2,3,4,5,6}).