Textbook Problem

In Problems 20-25, use the sum formulas I-V to express each of the following without the summation symbol. In Problems 20-23, find the numerical value.

$25.{\displaystyle \underset{i=1}{\overset{n}{\sum }}\left(1-\frac{2i}{n}+\frac{i^2}{n^2}\right)\left(\frac{3}{n}\right)}$