Merge pull request #169 from LibraryCarpentry/typos

assorted typos

Author: kylamj

episodes/01-format-data.md

@@ -167,7 +167,7 @@ We're going to take a messy version of some library training data and clean it u
 
 ## Important
 
-Do not forget of our first piece of advice:
+Do not forget our first piece of advice:
 **create a new file** for the cleaned data, and **never
 modify the original (raw) data**.
 

episodes/03-dates-as-data.md

@@ -172,7 +172,7 @@ sure that we are adding the amount to the correct entity.
 - Finally the complete date string is reconstructed using the `DATE()` function.
 
 **Note:** Time values raise similar challenges. Seconds can be directly
-added but to add hour and minutes you will need to make sure
+added but to add hours and minutes you will need to make sure
 that quantities are added to the correct entities.
 
 ## Advantages of Alternative Date Formatting

episodes/04-quality-control.md

@@ -59,7 +59,7 @@ keyboard) should never be entered. Likewise if one of the kinds of data being
 collected is a count, only integers greater than or equal to zero should be
 allowed.
 
-To control the kind of data entered into a a spreadsheet we use Data Validation
+To control the kind of data entered into a spreadsheet we use Data Validation
 (Excel) or Validity (LibreOffice Calc), to set the values that can be entered
 in each data column.