Mean ?

The mean of $$25$$ numbers is $$20$$. If $$5$$ is added to each of the first $$10$$ numbers, find the mean of new set of $$25$$ numbers.

Details and Assumptions:

The mean refers to the Arithmetic Mean. For example, the mean of the numbers $$1, 2$$ and $$3$$ is $$\frac{1+2+3}{3}=2$$.

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