Update _episodes/04-data-types-and-format.md

Author: orchid00

_episodes/04-data-types-and-format.md

@@ -18,7 +18,7 @@ keypoints:
     - Python uses two main data types text and numeric, these have a different names in basic Python and Pandas
     - Each column in a DataFrame has a shared data type for all rows
     - Any data type can be converted to another type
-    - You can discard or change null values
+    - Null values can be discarded or changed 
     - After manipulating a DataFrame you can save it in a CSV file
 
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