diff --git a/gradebook/.gitignore b/gradebook/.gitignore
new file mode 100644
index 0000000..38cf8cc
--- /dev/null
+++ b/gradebook/.gitignore
@@ -0,0 +1 @@
+*Book.txt
\ No newline at end of file
diff --git a/gradebook/src/GradeBook/Book.cs b/gradebook/src/GradeBook/Book.cs
index 58a0e03..186e120 100644
--- a/gradebook/src/GradeBook/Book.cs
+++ b/gradebook/src/GradeBook/Book.cs
@@ -56,7 +56,7 @@ namespace GradeBook
         {
             using(var writer = File.AppendText($"{Name}.txt"))
             {
-                writer.WriteLine("Test");
+                writer.WriteLine(grade);
                 if (GradeAdded != null)
                 {
                     GradeAdded(this, new EventArgs());
@@ -66,7 +66,19 @@ namespace GradeBook
 
         public override Statistics GetStatistics()
         {
-            throw new NotImplementedException();
+            var result = new Statistics();
+            using (var reader = File.OpenText($"{Name}.txt"))
+            {
+                var line = reader.ReadLine();
+                while(line != null)
+                {
+                    var number = double.Parse(line);
+                    result.Add(number);
+                    line = reader.ReadLine();
+                }
+            }
+
+            return result;
         }
     }
     public class InMemoryBook : Book, IBook
@@ -124,36 +136,10 @@ namespace GradeBook
         public override Statistics GetStatistics()
         {
             var result = new Statistics();
-            result.Average = 0.0;
-            result.highGrade = double.MinValue;
-            result.lowGrade = double.MaxValue;
 
             foreach (var grade in this.grades)
             {
-                result.lowGrade = Math.Min(grade, result.lowGrade);
-                result.highGrade = Math.Max(grade, result.highGrade);
-                result.Average += grade;
-            }
-
-            result.Average /= grades.Count;
-
-            switch (result.Average)
-            {
-                case var d when d >= 90.0:
-                    result.Letter = 'A';
-                    break;
-                case var d when d >= 80.0:
-                    result.Letter = 'B';
-                    break;
-                case var d when d >= 70.0:
-                    result.Letter = 'C';
-                    break;
-                case var d when d >= 60.0:
-                    result.Letter = 'D';
-                    break;
-                default:
-                    result.Letter = 'F';
-                    break;
+                result.Add(grade);
             }
 
             return result;
diff --git a/gradebook/src/GradeBook/Program.cs b/gradebook/src/GradeBook/Program.cs
index 96c4ad9..04e4f8e 100644
--- a/gradebook/src/GradeBook/Program.cs
+++ b/gradebook/src/GradeBook/Program.cs
@@ -8,7 +8,7 @@ namespace GradeBook
         static void Main(string[] args)
         {
 
-            var book = new InMemoryBook("Jason's Grade Book");
+            var book = new DiskBook("Jason's Grade Book");
             book.GradeAdded += OnGradeAdded;
 
             string input;
diff --git a/gradebook/src/GradeBook/Statistics.cs b/gradebook/src/GradeBook/Statistics.cs
index c743dd0..f800bb9 100644
--- a/gradebook/src/GradeBook/Statistics.cs
+++ b/gradebook/src/GradeBook/Statistics.cs
@@ -1,10 +1,54 @@
+using System;
+
 namespace GradeBook
 {
     public class Statistics
     {
-        public double Average;
+        public double Average
+        {
+            get
+            {
+                return Sum / Count;
+            }
+        }
         public double highGrade;
         public double lowGrade;
-        public char Letter;
+        public char Letter
+        {
+            get{
+                switch (Average)
+                {
+                    case var d when d >= 90.0:
+                        return 'A';
+                    case var d when d >= 80.0:
+                        return 'B';
+                    case var d when d >= 70.0:
+                        return 'C';
+                    case var d when d >= 60.0:
+                        return 'D';
+                    default:
+                        return 'F';
+                }
+            }
+        }
+        public double Sum;
+        public int Count;
+        
+        public void Add(double number)
+        {
+            Sum += number;
+            Count += 1;
+            
+            lowGrade = Math.Min(number, lowGrade);
+            highGrade = Math.Max(number, highGrade);
+        }
+
+        public Statistics()
+        {
+            Count = 0;
+            Sum = 0.0;
+            highGrade = double.MinValue;
+            lowGrade = double.MaxValue;
+        }
     }
 }
\ No newline at end of file