diff --git a/numpy_questions.py b/numpy_questions.py
index 07a10c1..62d000f 100644
--- a/numpy_questions.py
+++ b/numpy_questions.py
@@ -8,7 +8,7 @@
 The two functions below are skeleton functions. The docstrings explain what
 are the inputs, the outputs and the expected error. Fill the function to
 complete the assignment. The code should be able to pass the test that we
-wrote. To run the tests, use `pytest test_numpy_question.py` at the root of
+wrote. To run the tests, use `pytest test_numpy_questions.py` at the root of
 the repo. It should say that 2 tests ran with success.
 
 We also ask to respect the pep8 convention: https://pep8.org.
@@ -37,10 +37,14 @@ def max_index(X):
         If the input is not a numpy array or
         if the shape is not 2D.
     """
-    i = 0
-    j = 0
+    if not isinstance(X, np.ndarray):
+        raise ValueError("Input must be a numpy array.")
+    if X.ndim != 2:
+        raise ValueError("Input array must be 2D.")
 
-    # TODO
+    # Find the index of the maximum
+    flat_index = np.argmax(X)  # Get the index in the flattened array
+    i, j = divmod(flat_index, X.shape[1])  # Convert flat index to 2D index
 
     return i, j
 
@@ -62,6 +66,13 @@ def wallis_product(n_terms):
     pi : float
         The approximation of order `n_terms` of pi using the Wallis product.
     """
-    # XXX : The n_terms is an int that corresponds to the number of
-    # terms in the product. For example 10000.
-    return 0.
+    if n_terms == 0:
+        return 2
+
+    pi = 1
+    for n in range(1, n_terms+1):
+        numerateur = 4 * n ** 2
+        denominateur = numerateur - 1
+        pi *= numerateur / denominateur
+
+    return 2*pi