Simplify wording and rework example as doctest

Author: jiahao

doc/manual/mathematical-operations.rst

@@ -122,17 +122,21 @@ are::
     +=  -=  *=  /=  \=  %=  ^=  &=  |=  $=  >>>=  >>=  <<=
 
 
-It should be noted that updating operators can change the type of the variable.  For example, after the first 
-statement below, ``x`` is of type ``Uint32``, but after the second statement, it is of type ``Int``::
-
- 
-    x = 0x00000001
-    x *= 2
- 
- 
-This is in consistent with the equivalence between ``x *= 2`` and ``x = x * 2``: any assignment statement to
-a plain variable may change its type.
- 
+.. note::
+   Updating operators may change the type of the variable, since any assignment
+   statement to a plain variable may change its type.
+   
+   .. doctest::
+
+      julia> x = 0x01; typeof(x)
+      Uint8
+
+      julia> x *= 2 #Same as x = x * 2
+      2
+      
+      julia> isa(x, Int)
+      true
+
 .. _man-numeric-comparisons:
 
 Numeric Comparisons