diff --git a/exercises/ex03/.gitignore b/exercises/ex03/.gitignore
new file mode 100644
index 0000000..f1f00e5
--- /dev/null
+++ b/exercises/ex03/.gitignore
@@ -0,0 +1,2 @@
+.idea
+nlpwdlfw.egg-info
\ No newline at end of file
diff --git a/exercises/ex03/nlpwdlfw/__init__.py b/exercises/ex03/nlpwdlfw/__init__.py
deleted file mode 100644
index e69de29..0000000
diff --git a/exercises/ex03/nlpwdlfw/nodes.py b/exercises/ex03/nlpwdlfw/nodes.py
index b7cb48a..9f915e5 100644
--- a/exercises/ex03/nlpwdlfw/nodes.py
+++ b/exercises/ex03/nlpwdlfw/nodes.py
@@ -15,7 +15,7 @@ def __init__(self, arguments: List['ScalarNode']) -> None:
         for arg in self._arguments:
             arg._parents.append(self)
         # --- TASK_6 ---
-
+        self._cache = ScalarNodeCache()
         # --- TASK_6 ---
 
     def value(self) -> float:
@@ -32,7 +32,8 @@ def find_self_position_in_parents_arguments(self, parent: 'ScalarNode') -> int:
 
     def global_derivative_wrt_self(self) -> float:
         # --- TASK_6 ---
-
+        if self._cache.global_derivative_wrt_self is not None:
+            return self._cache.global_derivative_wrt_self
         # --- TASK_6 ---
 
         if len(self._parents) == 0:
@@ -42,11 +43,16 @@ def global_derivative_wrt_self(self) -> float:
             result = 0.0
             # --- TASK_5 ---
             # multiply and add (generalized chain rule)
+            for p in self._parents:
+                index_in_parents_arguments = self.find_self_position_in_parents_arguments(p)
+                parent_to_self_derivative = p.local_partial_derivatives_wrt_arguments()[index_in_parents_arguments]
+                parent_global_derivative = p.global_derivative_wrt_self()
 
+                result += parent_to_self_derivative * parent_global_derivative
             # --- TASK_5 ---
 
             # --- TASK_6 ---
-
+            self._cache.global_derivative_wrt_self = result
             # --- TASK_6 ---
 
             return result
@@ -66,18 +72,20 @@ class SumNode(ScalarNode):
 
     def value(self) -> float:
         # --- TASK_6 ---
-
+        if self._cache.value is not None:
+            return self._cache.value
         # --- TASK_6 ---
 
         result = 0.0
         # sum all arguments values
 
         # --- TASK_2 ---
-
+        for arg in self._arguments:
+            result += arg.value()
         # --- TASK_2 ---
 
         # --- TASK_6 ---
-
+        self._cache.value = result
         # --- TASK_6 ---
 
         return result
@@ -90,7 +98,7 @@ def local_partial_derivatives_wrt_arguments(self) -> List[float]:
         # dy/dw_3 = 1
 
         # --- TASK_2 ---
-        return None
+        return [1.0] * len(self._arguments)
         # --- TASK_2 ---
 
 
@@ -98,25 +106,28 @@ class ProductNode(ScalarNode):
 
     def value(self) -> float:
         # --- TASK_6 ---
-
+        if self._cache.value is not None:
+            return self._cache.value
         # --- TASK_6 ---
 
         result = 1.0
         # multiply all arguments values
 
         # --- TASK_3 ---
-
+        for arg in self._arguments:
+            result *= arg.value()
         # --- TASK_3 ---
 
         # --- TASK_6 ---
-
+        self._cache.value = result
         # --- TASK_6 ---
 
         return result
 
     def local_partial_derivatives_wrt_arguments(self) -> List[float]:
         # --- TASK_6 ---
-
+        if self._cache.local_partial_derivatives_wrt_arguments is not None:
+            return self._cache.local_partial_derivatives_wrt_arguments
         # --- TASK_6 ---
 
         # Partial derivative wrt. each argument is a product of all other arguments, for example
@@ -129,11 +140,17 @@ def local_partial_derivatives_wrt_arguments(self) -> List[float]:
         result = [0.0] * len(self._arguments)
 
         # --- TASK_3 ---
-
+        for i in range(len(self._arguments)):
+            ith_result = 1.0
+            for j in range(len(self._arguments)):
+                if i != j:
+                    j_value = self._arguments[j].value()
+                    ith_result *= j_value
+            result[i] = ith_result
         # --- TASK_3 ---
 
         # --- TASK_6 ---
-
+        self._cache.local_partial_derivatives_wrt_arguments = result
         # --- TASK_6 ---
 
         return result
diff --git a/exercises/ex03/tests/__init__.py b/exercises/ex03/tests/__init__.py
deleted file mode 100644
index e69de29..0000000
diff --git a/exercises/ex03/tests/test_nodes.py b/exercises/ex03/tests/test_nodes.py
index 41205c9..7dca665 100644
--- a/exercises/ex03/tests/test_nodes.py
+++ b/exercises/ex03/tests/test_nodes.py
@@ -8,7 +8,7 @@ class TestNodes(TestCase):
     def test_task1(self):
         value = 2
         # --- TASK_1 ---
-        
+        value = 1
         # --- TASK_1 ---
         self.assertEqual(1, value)
 
@@ -47,7 +47,12 @@ def test_task4(self):
         # dummy initialization
         a, b, one, r, s, e = [ConstantNode(1)] * 6
         # --- TASK_4 ---
-
+        a = ConstantNode(2)
+        b = ConstantNode(3)
+        one = ConstantNode(1)
+        r = SumNode([a, b])
+        s = SumNode([b, one])
+        e = ProductNode([r, s])
         # --- TASK_4 ---
 
         # test that b has two parents