Answer:
3/7
Step-by-step explanation:
Probability is essentially (# ways specific event can occur) / (# ways any general event can occur).
In this case, the specific event is getting a human avatar. Since there are 3 humans to choose from, the number of ways this specific event can occur is 3 ways. The general event is just choosing any avatar. Since there are a total of 3 + 4 = 7 characters to select from, the number of ways this general event can occur is 7.
Putting it together, we have the probability of choosing a human character as 3/7.