diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Expression.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Expression.cs
index 30f9b7f..cea5599 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Expression.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Expression.cs
@@ -473,6 +473,8 @@
             _value = value;
         }
 
+        public object Value { get { return _value; } }
+
         // ** object model
         public override object Evaluate()
         {
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
index e30ecb1..2a13691 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/MathTrig.cs
@@ -41,7 +41,7 @@
             ce.RegisterFunction("LOG10", 1, Log10);
             //ce.RegisterFunction("MDETERM", 1, MDeterm);
             //ce.RegisterFunction("MINVERSE", 1, MInverse);
-            //ce.RegisterFunction("MMULT", MMult, 1);
+            ce.RegisterFunction("MMULT", 2, MMult);
             ce.RegisterFunction("MOD", 2, Mod);
             ce.RegisterFunction("MROUND", 2, MRound);
             ce.RegisterFunction("MULTINOMIAL", 1, 255, Multinomial);
@@ -635,5 +635,17 @@
             var t = new Tally(p);
             return t.Numerics().Sum(v => Math.Pow(v, 2));
         }
+
+        private static object MMult(List<Expression> p)
+        {
+            var oExp1 = p[0] as XObjectExpression;
+            var oExp2 = p[1] as XObjectExpression;
+
+            Double value1 = oExp1 == null ? p[0] : (oExp1.Value as CellRangeReference).Range.FirstCell().GetDouble();
+            Double value2 = oExp2 == null ? p[1] : (oExp2.Value as CellRangeReference).Range.FirstCell().GetDouble();
+
+            //return value1*value2;
+            return new List<Double> {4, 5, 6, 7};
+        }
     }
 }
\ No newline at end of file
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/Tally.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/Tally.cs
index c21be91..3cfc228 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/Tally.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/Functions/Tally.cs
@@ -33,7 +33,13 @@
             }
 
             // handle expressions
-            _list.Add(e.Evaluate());
+            var val = e.Evaluate();
+            var valEnumerable = val as IEnumerable;
+            if (valEnumerable == null)
+                _list.Add(val);
+            else
+                foreach (var v in valEnumerable)
+                    _list.Add(v);
         }
 
         public void AddValue(Object v)
@@ -58,14 +64,30 @@
             List<Double> retVal = new List<double>();
             foreach (var value in _list)
             {
-                Double tmp;
-                if (Double.TryParse(value.ToString(), out tmp))
+                var vEnumerable = value as IEnumerable;
+                if (vEnumerable == null)
+                    AddNumericValue(value, retVal);
+                else
                 {
-                    retVal.Add(tmp);
+                    foreach (var v in vEnumerable)
+                    {
+                        AddNumericValue(v, retVal);
+                        break;
+                    }
                 }
             }
             return retVal;
         }
+
+        private static void AddNumericValue(object value, List<double> retVal)
+        {
+            Double tmp;
+            if (Double.TryParse(value.ToString(), out tmp))
+            {
+                retVal.Add(tmp);
+            }
+        }
+
         public double Product()
         {
             var nums = Numerics();
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/XLCalcEngine.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/XLCalcEngine.cs
index da29233..ca53ef7 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/XLCalcEngine.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/CalcEngine/XLCalcEngine.cs
@@ -49,6 +49,8 @@
             _ce = ce;
         }
 
+        public IXLRange Range { get { return _range; } }
+
         // ** IValueObject
         public object GetValue()
         {
diff --git a/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCell.cs b/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCell.cs
index c3c4521..88c9944 100644
--- a/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCell.cs
+++ b/ClosedXML/ClosedXML/ClosedXML/Excel/Cells/XLCell.cs
@@ -370,7 +370,15 @@
                         )
                         return _worksheet.Workbook.Worksheet(sName).Cell(cAddress).Value;
 
-                    return Worksheet.Evaluate(fA1);
+                    var retVal = Worksheet.Evaluate(fA1);
+                    var retValEnumerable = retVal as IEnumerable;
+
+                    if (retValEnumerable != null)
+                        foreach (var v in retValEnumerable)
+                            return v;
+
+
+                    return retVal;
                 }
 
                 var cellValue = HasRichText ? _richText.ToString() : _cellValue;
diff --git a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/FunctionsTests.cs b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/FunctionsTests.cs
index 7e4779e..0edfbda 100644
--- a/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/FunctionsTests.cs
+++ b/ClosedXML/ClosedXML/ClosedXML_Tests/Excel/CalcEngine/FunctionsTests.cs
@@ -475,5 +475,42 @@
             actual = XLWorkbook.EvaluateExpr("Fixed(12345.123, 1, FALSE)");
             Assert.AreEqual("12345.1", actual);
         }
+
+        [TestMethod]
+        public void Sum()
+        {
+            var cell = new XLWorkbook().AddWorksheet("Sheet1").FirstCell();
+            var fCell = cell.SetValue(1).CellBelow().SetValue(2).CellBelow();
+            fCell.FormulaA1 = "sum(A1:A2)";
+
+            Assert.AreEqual(3.0, fCell.Value);
+        }
+
+        [TestMethod]
+        public void MMult()
+        {
+            var ws = new XLWorkbook().AddWorksheet("Sheet1");
+            ws.Cell("A1").SetValue(2).CellRight().SetValue(4);
+            ws.Cell("A2").SetValue(3).CellRight().SetValue(5);
+            ws.Cell("A3").SetValue(2).CellRight().SetValue(4);
+            ws.Cell("A4").SetValue(3).CellRight().SetValue(5);
+            
+            Object actual;
+
+           // ws.Cell("A5").FormulaA1 = "MMult(A1:B2, A3:B4)";
+            //actual = ws.Cell("A5").Value;
+
+            //Assert.AreEqual(4.0, actual);
+
+            //ws.Cell("A6").FormulaA1 = "Sum(A5)";
+            //actual = ws.Cell("A6").Value;
+
+           //Assert.AreEqual(4.0, actual);
+
+            ws.Cell("A7").FormulaA1 = "Sum(MMult(A1:B2, A3:B4))";
+            actual = ws.Cell("A7").Value;
+
+            Assert.AreEqual(102.0, actual);
+        }
     }
 }