\(\dfrac{13}{17}-\dfrac{23}{31}+\dfrac{4}{17}-\dfrac{8}{31}\)
\(=\left(\dfrac{13}{17}+\dfrac{4}{17}\right)-\left(\dfrac{23}{31}+\dfrac{8}{31}\right)\)
\(=\dfrac{17}{17}-\dfrac{31}{31}\)
\(=1-1\)
\(=0\)
13/17 - 23/31 + 4/17- 8/31
= (13/17 + 4/17) - (23/31 - 8/31)
= 1 - 15/31
= 16/31