98 -20%

$${\mathtt{98}}{\mathtt{\,-\,}}{\mathtt{20}}\% = {\frac{{\mathtt{392}}}{{\mathtt{5}}}} = {\mathtt{78.4}}$$

100% - 20% = 80% = 80/100 = 0,8

98 fr * 0,8 = 78,40 fr

20% von 98 fr  =  $${\frac{{\mathtt{20}}{\mathtt{\,\times\,}}{\mathtt{98}}}{{\mathtt{100}}}} = {\frac{{\mathtt{98}}}{{\mathtt{5}}}} = {\mathtt{19.6}}$$   fr     =>  98 fr -19,6 fr = 78,40 fr

Gruß radix !