\(\dfrac{7}{21}+\dfrac{17}{25}-\dfrac{20}{15}+\dfrac{3}{4}+\dfrac{8}{25}\)
\(=\dfrac{1}{3}+\dfrac{17}{25}-\dfrac{4}{3}+\dfrac{3}{4}+\dfrac{8}{25}\)
\(=\left(\dfrac{1}{3}-\dfrac{4}{3}\right)+\left(\dfrac{17}{25}+\dfrac{8}{25}\right)+\dfrac{3}{4}\)
\(=-1+1+\dfrac{3}{4}\)
\(=\dfrac{3}{4}\)