diff --git a/numpy_questions.py b/numpy_questions.py
index 07a10c1..5669872 100644
--- a/numpy_questions.py
+++ b/numpy_questions.py
@@ -37,11 +37,12 @@ def max_index(X):
         If the input is not a numpy array or
         if the shape is not 2D.
     """
-    i = 0
-    j = 0
-
-    # TODO
+    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.")
 
+    i, j = np.unravel_index(np.argmax(X), X.shape)
     return i, j
 
 
@@ -64,4 +65,13 @@ def wallis_product(n_terms):
     """
     # XXX : The n_terms is an int that corresponds to the number of
     # terms in the product. For example 10000.
-    return 0.
+    # return 0.
+
+    if n_terms == 0:
+        return 2
+
+    p = 1
+    for n in range(1, n_terms+1):
+        p *= (4*n**2) / (4*n**2 - 1)
+
+    return 2*p