Question about a class

New to OOPS and VB.NET

I am trying to design a class called 'RATE'
The rate object can be a "simple rate" or "Complex rate". The attributes of both simple rate and complex rate are exactly same. Its just that the complex rate is summation of 2 or more simple rate objects.

Design question:
1. since both the simple rate and complex rate have same charecteristics. I probably should design only once class called as 'RATE' class which has the interfaces and implementation.
Is that correct way of thinking?

2. The calling object/function should be intelligent enough to decide when it needs a simple rate or complex rate. And if it need an simple rate object it will instantiate only object of the 'Rate' class and if it decides that it needs a complex rate then 2 or 3 instances of 'RATE' class should be instantiated.
Is that correct way of thinking?

OR should I create an abstract 'RATE' class and create 2 derived classess called 'Simple Rate' and 'Complex rate"

Quote:

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OR should I create an abstract 'RATE' class and create 2 derived classess called 'Simple Rate' and 'Complex rate"

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I would probably choose this option - even though it might seem like overkill for such a simple class it does fit in better with the OO model

while I am learning how to implement OOPS concepts (abstraction, inheritance, overloading ...ect) in vb.net , I am reading UML books.

Where does the concepts UML fit in OOP? Like say "Composition" relationship between classess. According to the definition of composition if there is parent-child relationship. Container class and contained class.
say for example "Bank" is a class and "Bank Account" is another class. with out "Bank" class there can't be a "Bank Account" class and there can be many "Bank account" classess for each "Bank class". Is there a specific way we can implement the various relationships of classess in VB.NET? where does the INHERITANCE fit into all the UML concepts? Pls help me out here ..thank you