using System;

using System.Collections.Generic;

using System.Linq;

​

public class Program

{

    public static void Main()

    {

        var products = new List<Product>()

        {new Product() {ProductID = 1, ShopID = 1, Amount = 1000, Price = 220, AddedDate = DateTime.Parse("2020-07-01")}, 

         new Product() {ProductID = 1, ShopID = 1, Amount = 1000, Price = 230, AddedDate = DateTime.Parse("2020-07-30")}, 

         new Product() {ProductID = 1, ShopID = 1, Amount = 100, Price = 21, AddedDate = DateTime.Parse("2020-07-10")},

         new Product() {ProductID = 1, ShopID = 1, Amount = 100, Price = 22, AddedDate = DateTime.Parse("2020-07-31")}, 

         new Product() {ProductID = 1, ShopID = 2, Amount = 100, Price = 23, AddedDate = DateTime.Parse("2020-07-10")},

         new Product() {ProductID = 1, ShopID = 2, Amount = 100, Price = 20, AddedDate = DateTime.Parse("2020-07-12")},

        };

        decimal lowestPrice = (from s1 in products

                                where (from s2 in products

                                       group s2 by new { s2.ShopID, s2.Amount } into g

                                       select (g.Max(s2 => s2.AddedDate))

                                    ).Contains(s1.AddedDate)

                                select (s1.Price / s1.Amount))

                                .Min();

         decimal highestPrice = (from s1 in products

                                where (from s2 in products

                                       group s2 by new { s2.ShopID, s2.Amount } into g

                                       select (g.Max(s2 => s2.AddedDate))

                                    ).Contains(s1.AddedDate)

                                select (s1.Price / s1.Amount))

                                .Max();

        Console.WriteLine("Lowest price: " + lowestPrice);

        Console.WriteLine("Highest price: " + highestPrice);

    }

}

​

internal class Product

{

    public int ProductID

    {

        get;

        set;

    }

​

    public int ShopID

    {

        get;

        set;

    }

​

    public decimal Amount

    {

        get;

        set;

    }

​

    public decimal Price

    {

        get;

        set;

    }

​

    public DateTime AddedDate

    {

        get;

        set;

    }

}