def determine_grade(scores):
    if scores >= 90 and <= 100:
        return 'A'
    elif scores >= 80 and <= 89:
        return 'B'
    elif scores >= 70 and <= 79:
        return 'C'
    elif scores >= 60 and <= 69:
        return 'D'
    elif scores >= 50 and <= 59:
        return 'E'
    else:
        return 'F'