fix numbering in input_output and Modules_and_Packages

source/Input_Output.rst

 .. sectnum::
-   :start: 10
+   :start: 9
 
 .. _Input_Output:
 

source/Modules_and_Packages.rst

 .. sectnum::
-   :start: 9
+   :start: 10
 
 .. _Modules_and_Packages:
 
@@ -16,7 +16,7 @@ Exercise
 
 Write a program that calculates the similarity of 2 RNA sequences.
 
-* To compute the simalirity you need to parse a file containing the :download:`similarity matrix <_static/data/similarity_matrix>`.
+* To compute the similarity you need to parse a file containing the :download:`similarity matrix <_static/data/similarity_matrix>`.
   **Hint**: use the module containing the functions that handle a matrix from previous chapter.
   put this matrix.py file in a directory named "my_python_lib" in your home or Desktop
   and import it in your current program (the similarity script must be placed elsewhere).