MathDrill.cs

class Program
{
    static void Main(string[] args)
    {
        var r = new Random();
        for (int i = 0; i < 10; i++)
        {
            var a = r.Next(1, 10);
            var b = r.Next(1, 10);
            Console.Write($"{a} + {b} = ");
            Console.WriteLine(int.TryParse(Console.ReadLine(), out var input) && input == a + b ? 
                "正解！" : 
                $"不正解！答え: {a + b}");
        }
    }
}