No. In method overriding the behaviour of overrided method 
is different. The subclass override only those methods, 
which has different behaviour than superclass else alawys 
use all the methods of superclass, which is better than 
making a lot duplication by defining another class for same 
methods of superclass.

yes

No.In subclass we will extend the functionality of super
class method.

To understand the Question, one needs to know the scenarios 
where in a method is overriden.
there are two cases:
you want to override a method:
1)when the super class doesnt know how to implement it, and 
leaves the implementation to the sub-class.
2)when the subclass feels, it has to add few more details 
specific to itself than which are provided by the 
superclass.

so there is no duplication happening provided one overrides 
a method sensibly(understanding thorougly if overriding a 
method is necessary or not).if one wishes to write things 
that are already available, it is then called "duplication 
of code",