Actually, you have to answer something more from the other side: for a randomly picked person (voter), i.e. considering the distribution of race, gender and age

Actually, you have to answer something more from the other side: for a randomly picked person (voter), i.e. considering the distribution of race, gender and age in the population: how likely is a guess just based on these factors correct. The number you come up with might actually not be as far from 50% as you would expect.