def convert_grade_to_letter(grade: float) -> str:
    """
    Convert a numeric grade to a letter grade.

    Rules
    -----
    A valid grade is a number from 0 to 100 inclusive:

    - 'A': 90 to 100
    - 'B': 80 to 89
    - 'C': 70 to 79
    - 'D': 60 to 69
    - 'F': below 60

    Any number outside 0 to 100, above or below, is not a valid grade and
    returns 'Grade is invalid'.

    Parameters
    ----------
    grade : float
        The numeric grade to convert.

    Returns
    -------
    str
        'A', 'B', 'C', 'D', 'F', or 'Grade is invalid'.

    Examples
    --------
    >>> convert_grade_to_letter(92)
    'A'
    >>> convert_grade_to_letter(85)
    'B'
    >>> convert_grade_to_letter(58)
    'F'
    >>> convert_grade_to_letter(105)
    'Grade is invalid'
    """
    raise NotImplementedError("Replace this line with your code.")