Even a set can be sincere, why not you?

Calvin calls a set of any five consecutive positive integers (each less than 100) as sincere if their sum ends with the digit 5.

If the probability that a given set of any five consecutive positive integers (each less than 100) is sincere can be expressed as $$\dfrac{a}{b}$$, where $$a$$ and $$b$$ are coprime positive integers, then find the value of $$a+b$$.

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