The sample space has 36 outcomes from (1, 1) to (6, 6). The outcomes for the event are the pairs that sum to 7: {(1, 6), (2, 5), (3, 4), (4, 3), (5, 2), (6, 1)}. There are six outcomes in this event. So $\displaystyle\frac{{6}}{{36}}\usepackage{cmbright}\Huge\$ , or $\displaystyle\frac{{1}}{{6}}\usepackage{cmbright}\Huge\$ , is the probability of rolling a sum of 7.