RunTasksParallelly.cs

class Program
{
    static void Main(string[] args)
    {
        var stopwatch = new Stopwatch();
        stopwatch.Start();

        RunParallelly().Wait();

        stopwatch.Stop();
        Console.WriteLine(stopwatch.Elapsed); // 1초
        Console.ReadLine();
    }

    private static async Task RunParallelly()
    {
        var startedTask = Foo();
        await Bar();
        await startedTask;
    }

    private static async Task<int> Foo()
    {
        await Task.Delay(1000);
        return 10;
    }

    private static async Task<string> Bar()
    {
        await Task.Delay(1000);
        return "bar";
    }
}