using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    private static List<Model> _lista = new List<Model>

    {

        new Model { Data = new DateTime(2017, 12, 04), FatorDiario = 1.02077M },

        new Model { Data = new DateTime(2017, 12, 05), FatorDiario = 1.03006M },

        new Model { Data = new DateTime(2017, 12, 06), FatorDiario = 1.04563M },

        new Model { Data = new DateTime(2017, 12, 07), FatorDiario = 1.03328M }

    };

    public static void Main()

    {

        DateTime inicio = new DateTime(2017, 12, 05);

        DateTime fim = new DateTime(2017, 12, 07);

        var s = _lista.Where(model => model.Data >= inicio && model.Data <= fim)

                      .Select(model => model.FatorDiario)

                      .Aggregate((a, b) => a * b);

        Console.WriteLine(s);

    }

}

​

public class Model

{

    public DateTime Data;

    public decimal FatorDiario;

}