diff --git a/stacks_queues/n_stacks/n_stacks_challenge.ipynb b/stacks_queues/n_stacks/n_stacks_challenge.ipynb
index 545ddc3..971e560 100644
--- a/stacks_queues/n_stacks/n_stacks_challenge.ipynb
+++ b/stacks_queues/n_stacks/n_stacks_challenge.ipynb
@@ -43,6 +43,8 @@
     "* Does popping from an empty stack result in an exception?\n",
     "    * Yes\n",
     "* Can we assume the user passed in stack index is valid?\n",
+    "    * Yes\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
diff --git a/stacks_queues/n_stacks/n_stacks_solution.ipynb b/stacks_queues/n_stacks/n_stacks_solution.ipynb
index acdbe6a..47a6cd3 100644
--- a/stacks_queues/n_stacks/n_stacks_solution.ipynb
+++ b/stacks_queues/n_stacks/n_stacks_solution.ipynb
@@ -42,6 +42,8 @@
     "* Does popping from an empty stack result in an exception?\n",
     "    * Yes\n",
     "* Can we assume the user passed in stack index is valid?\n",
+    "    * Yes\n",
+    "* Can we assume this fits memory?\n",
     "    * Yes"
    ]
   },
@@ -118,8 +120,8 @@
     "    def __init__(self, num_stacks, stack_size):\n",
     "        self.num_stacks = num_stacks\n",
     "        self.stack_size = stack_size\n",
-    "        self.stack_pointers = [-1] * num_stacks\n",
-    "        self.stack_array = [None] * num_stacks * stack_size\n",
+    "        self.stack_pointers = [-1] * self.num_stacks\n",
+    "        self.stack_array = [None] * self.num_stacks * self.stack_size\n",
     "\n",
     "    def abs_index(self, stack_index):\n",
     "        return stack_index * self.stack_size + self.stack_pointers[stack_index]\n",