using System;

using System.Collections.Generic;

using System.Linq;

​

 public class Rates

    {

        public string RateClass { get; set; }

        public decimal CostDay { get; set; }

        public decimal CostWeek { get; set; }

    }

public class Program

{

    public static void Main()

    {

           var rates = new List<Rates>

            {

                new Rates {CostDay = 2, CostWeek = 7, RateClass = "Test 1"},

                new Rates {CostDay = 4, CostWeek = 17, RateClass = "Test 1"},

                new Rates {CostDay = 6, CostWeek = 27, RateClass = "Test 2"},

                new Rates {CostDay = 8, CostWeek = 37, RateClass = "Test 2"}

            };

​

            var data = rates.GroupBy(t => t.RateClass)

                .Select(g => new Rates {

                    RateClass = g.Key,

                    CostDay = g.Min(x => x.CostDay),

                    CostWeek = g.Sum(x => x.CostWeek)

                })

                .ToList();

        foreach(var r in data){

        Console.WriteLine(r.RateClass + ", CostDay: " + r.CostDay + ", CostWeek: " + r.CostWeek);   

        }

    }

}