from typing import List
from typing import Dict


def probability_of(pairings: List[Dict], a: str, b: str) -> float:
    """
    Return the probability that `a` and `b` are together.

    Parameters
    ----------
    pairings : List[Dict]
        A list of possible pairings. Each dictionary should be a mapping of
        each contestant's name to the contestant they are paired with.
    a : str
        The name of a contestant
    b : str
        The name of another contestant
    """
    return sum([p[a] == b for p in pairings]) / len(pairings)