$${\frac{\left({\mathtt{5}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{2}}}{{\mathtt{3}}}}\right)}{{\mathtt{8}}}} = {\frac{{\mathtt{17}}}{{\mathtt{24}}}} = {\mathtt{0.708\: \!333\: \!333\: \!333\: \!333\: \!3}}$$
http://web2.0rechner.de/#(5+2/3) / (8)
http://www.free-education-resources.com/www.mathematik.net//0-tabellen/zahlenbereiche.htm
http://www.mathematik-wissen.de/definition_rationale_zahlen.htm