Well, the triangle could have a few possibilities to get the angles. They are: 30-30-120 30-60-90 30-90-60 30-120-30 60-30-90 60-60-60 60-90-30 90-30-60 90-60-30 Thus, there are 9 possible cases. Out of them 3 are good, so the probability is 1/3, or 33%.