public override Statistics GetStatistics()
        {
            var result = new Statistics();

            foreach (var grade in grades)
            {
                result.AddNum(grade);
            }
            return(result);
        }
        public override Statistics GetStatistics()
        {
            var result = new Statistics();

            using (var bookFile = File.OpenText($"{Name}.txt"))
            {
                while (true)
                {
                    var line = bookFile.ReadLine();
                    if (line == null)
                    {
                        break;
                    }
                    else
                    {
                        var grade = double.Parse(line);
                        result.AddNum(grade);
                    }
                }
                return(result);
            }
        }