public static class DecimalHelpers
    {
        /// <summary>
        /// Format a decimal XX.XX to XX,XX%.
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public static string FormatToStringPercentageValue(this decimal value)
        {
            return value.ToString().Replace(".", ",").FormatToPercentageValue();
        }
    }
    
    public static class StringHelpers
    {
        /// <summary>
        /// Add % at the end of the string.
        /// </summary>
        /// <param name="value"></param>
        /// <returns></returns>
        public static string FormatToPercentageValue(this string value)
        {
            return string.Concat(value, "%");
        }
    }