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"