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Getting Exact precision of decimal places from a double in .NET 3.5
double myDoubleValue = 50234.9489898997952932;

using System.Globalization;

class Program
{
    static void Main(string[] args)
    {
        double d = 50234.9489898997952932;
        char probablyDot = CultureInfo.CurrentCulture.NumberFormat.NumberDecimalSeparator[0];
        string[] number = d.ToString().Split(probablyDot);


        //Console.WriteLine(number[0] + probablyDot + number[1].Remove(4));

        Console.WriteLine(number[0] + probablyDot + (number.Length >1 ? (number[1].Length>4? number[1].Substring(0,4):number[1]): "0000"));
        //Output: 50234.9489

        Console.ReadKey();
    }
}

double d = 50234.94895345345345;
var Expected_result =  Double.Parse((Regex.Match(d.ToString(), "[+-]?\d*.\d{0,4}")).Value);

public static class DoubleEx
{
    public static double TruncateFraction(this double value, int fractionRound)
    {
        double factor = Math.Pow(10, fractionRound);
        return Math.Truncate(value * factor) / factor;
    }
}

double foo = 50234.9489898997952932;
double bar = foo.TruncateFraction(4);

Console.WriteLine(foo); //50234.9489898997952932
Console.WriteLine(bar); //50234.9489

private static string TrimDecimalPlaces(double value, int numberOfDecimalPlaces)
{
    string valueString = value.ToString();

    if (!valueString.Contains(".")) return valueString;

    int indexOfDot = valueString.IndexOf(".");

    if ((indexOfDot + numberOfDecimalPlaces + 1) < valueString.Length)
    {
        return valueString.Remove(indexOfDot + numberOfDecimalPlaces + 1);
    }
    return valueString;
}