diff --git a/conferences/13-inheritance/accounting/Cart.cs b/conferences/13-inheritance/accounting/Cart.cs
index ea03444..fb9a17d 100644
--- a/conferences/13-inheritance/accounting/Cart.cs
+++ b/conferences/13-inheritance/accounting/Cart.cs
@@ -1,4 +1,5 @@
-namespace Accounting
+using System;
+namespace Accounting
 {
     public class Cart
     {
@@ -31,7 +32,11 @@ public virtual IEnumerable<Product> Products()
 
         public void Add(Product product)
         {
-            this.products.Add(product);
+            int index = products.FindIndex(p => p.Name == product.Name && p.GetType() == product.GetType());
+            if (index == -1)
+                this.products.Add();
+            else
+                this.products[index].AddUnits(product.Units);
         }
     }
 
diff --git a/conferences/13-inheritance/accounting/Product.cs b/conferences/13-inheritance/accounting/Product.cs
index 3c0e0d4..9791a96 100644
--- a/conferences/13-inheritance/accounting/Product.cs
+++ b/conferences/13-inheritance/accounting/Product.cs
@@ -18,13 +18,18 @@ public virtual int TotalCost()
             return this.Price * this.Units;
         }
 
+        public virtual void AddUnits(int units)
+        {
+            this.Units += units;
+        }
+
         public override string ToString()
         {
             return $"{this.Name} - ${this.Price} (x{this.Units}) = ${this.TotalCost()}";
         }
     }
 
-    public class DiscountProduct: Product
+    public class DiscountProduct : Product
     {
         public double Discount { get; private set; }
 
diff --git a/conferences/13-inheritance/app/Program.cs b/conferences/13-inheritance/app/Program.cs
index e89f056..ee6de10 100644
--- a/conferences/13-inheritance/app/Program.cs
+++ b/conferences/13-inheritance/app/Program.cs
@@ -8,8 +8,8 @@ class Program
         new Product("🐟 Pescado (kg)", 100, 10),
         new Product("🐔 Pollo (kg)", 150, 1),
         new Product("🐔 Pollo (kg)", 150, 5),
-        new Product("🥚 Huevo", 10, 1),
-        new Product("🥚 Huevos (caja)", 10, 30),
+        new Product("🥚 Huevos (unidades)", 10, 1),
+        new Product("🥚 Huevos (unidades)", 10, 30),
     };
 
     static void Main()