\documentclass[a4paper,11pt]{article}

\usepackage{ngerman}
\usepackage{amsmath,amsfonts,amssymb,amsthm}

\usepackage{tikz}
\usetikzlibrary{arrows,chains,matrix,positioning,scopes}
\usetikzlibrary{arrows.meta}
\usetikzlibrary{math}

\def\O{\mathcal{O}}
\def\sort{\mathrm{sort}}
\def\scan{\mathrm{scan}}
\def\dist{\mathrm{dist}}
\def\Z{\mathbb{Z}}
\def\Q{\mathbb{Q}}
\def\R{\mathbb{R}}
\def\E{\mathbb{E}}


\begin{document}


\textbf{Aufgabe 1}
\begin{center}
	\begin{tikzpicture}
	[->,>=triangle 45,shorten >=1pt,every node/.style={circle,inner sep=1pt,minimum size=4pt},font=\large]
	\node[draw=black,fill] (a) at (2,4) {};
	\node[draw=black,fill] (b) at (4,4) {};
	\node[draw=black,fill,label=left:{\Large$s$}]  (c) at (1,2) {};
	\node[draw=black,fill] (d) at (3,2) {};
	\node[draw=black,fill,label=right:{\Large$t$}] (e) at (5,2) {};
	\node[draw=black,fill] (f) at (2,0) {};
	\node[draw=black,fill] (g) at (4,0) {};
	
	\path
	(c) edge node[above left] {$0.5$} (a) edge node[above] {$0.1$} (d) edge node[below left] {$0.4$} (f)
	(a) edge node[above] {$0.5$} (b)
	(b) edge node[above right] {$0.3$} (e) edge node[above left] {$0.2$} (d)
	(d) edge node[above right] {$0$} (a) edge node[above] {$0.4$} (e) edge node[above left] {$0.3$} (f)
	(f) edge node[below] {$0.7$} (g)
	(g) edge node[above right] {$0.4$} (d) edge node[below right] {$0.3$} (e)
	;
	\end{tikzpicture}
\end{center}


\end{document}