diff --git a/chap6_essential_tools_for_mvc/NinjectDemo/Program.cs b/chap6_essential_tools_for_mvc/NinjectDemo/Program.cs
index 4e013f4..a626bcc 100644
--- a/chap6_essential_tools_for_mvc/NinjectDemo/Program.cs
+++ b/chap6_essential_tools_for_mvc/NinjectDemo/Program.cs
@@ -35,10 +35,16 @@ namespace NinjectDemo
 
     public class DefaultDiscountHelper : IDiscountHelper
     {
-        public decimal DiscountSize { get; set; }
+        private decimal discountRate;
+
+        public DefaultDiscountHelper(decimal discountParam)
+        {
+            discountRate = discountParam;
+        }
+        
         public decimal ApplyDiscount(decimal totalParam)
         {
-            return (totalParam - (DiscountSize * totalParam));
+            return (totalParam - (discountRate / 100m * totalParam));
         }
     }
 }