He has $=\textbackslash$5\times8=\textbackslash$40$  Number of $\textbackslash$2$-notes $=\textbackslash$40\div\textbackslash$2=20$ 
Paul had eight $$\textbackslash$5$$-notes at first. He exchanged all his money for $$\textbackslash$2$$-notes only. How many notes did he have in the end? 
[1] $$16$$ 
[2] $$20$$ 
[3] $$40$$ 
[4] $$80$$ 