diff --git a/gradebook/src/GradeBook/Book.cs b/gradebook/src/GradeBook/Book.cs
index 3c8262a..caee2f5 100644
--- a/gradebook/src/GradeBook/Book.cs
+++ b/gradebook/src/GradeBook/Book.cs
@@ -19,6 +19,25 @@ namespace GradeBook
             this.grades.Add(grade);
         }
 
+        public void AddLetterGrade(char letter)
+        {
+            switch (letter)
+            {
+                case 'A':
+                    AddGrade(90);
+                    break;
+                case 'B':
+                    AddGrade(80);
+                    break;
+                case 'C':
+                    AddGrade(70);
+                    break;
+                default:
+                    AddGrade(0);
+                    break;
+            }
+        }
+
         public Statistics GetStatistics()
         {
             var result = new Statistics();
@@ -26,21 +45,21 @@ namespace GradeBook
             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;
-            // }
-
-            var index = 0;
-            do
+            foreach (var grade in this.grades)
             {
-                result.lowGrade = Math.Min(grades[index], result.lowGrade);
-                result.highGrade = Math.Max(grades[index], result.highGrade);
-                result.Average += grades[index];
-                index += 1;
-            } while (index < grades.Count);
+                result.lowGrade = Math.Min(grade, result.lowGrade);
+                result.highGrade = Math.Max(grade, result.highGrade);
+                result.Average += grade;
+            }
+
+            // var index = 0;
+            // do
+            // {
+            //     result.lowGrade = Math.Min(grades[index], result.lowGrade);
+            //     result.highGrade = Math.Max(grades[index], result.highGrade);
+            //     result.Average += grades[index];
+            //     index += 1;
+            // } while (index < grades.Count);
 
             result.Average /= grades.Count;
             return result;