Update tour.md (dotnet#3401)

Author: isaacabraham

docs/fsharp/tour.md

@@ -195,7 +195,7 @@ Tuples are great for returning multiple values from a function, and using an ad-
 
 Records are a "step up" from Tuples, having named labels and support for optional members.  They are great for a low-ceremony representation of data in-transit through your program.  Because they have structural equality, they are easy to use with comparison.
 
-Discriminated Unions have many reasons, but the core benefit is to be able to utilize them in conjunction with Pattern Matching to account for all possible "shapes" that a data can have.  
+Discriminated Unions have many uses, but the core benefit is to be able to utilize them in conjunction with Pattern Matching to account for all possible "shapes" that a data can have.  
 
 Classes are great for a huge number of reasons, such as when you need to represent information and also tie that information to functionality.  As a rule of thumb, when you have functionality which is conceptually tied to some data, using Classes and the principles of Object-Oriented Programming is a big benefit.  Classes are also the preferred data type when interoperating with C# and Visual Basic, as these languages use classes for nearly everything.