1 2/5 multiplizieren um 0,4 zu erhalten

(1+2/5) *x = 0,4     ->    x =  0.4 / (1+2/5)     ->  x = 2/7

$${\frac{{\mathtt{0.4}}}{\left({\mathtt{1}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{2}}}{{\mathtt{5}}}}\right)}} = {\frac{{\mathtt{2}}}{{\mathtt{7}}}} = {\mathtt{0.285\: \!714\: \!285\: \!714\: \!285\: \!7}}$$

$${\frac{\left({\mathtt{1}}{\mathtt{\,\small\textbf+\,}}{\frac{{\mathtt{2}}}{{\mathtt{5}}}}\right){\mathtt{\,\times\,}}{\mathtt{2}}}{{\mathtt{7}}}} = {\frac{{\mathtt{2}}}{{\mathtt{5}}}} = {\mathtt{0.4}}$$

Gruß Radix ! ( und eine gute Nacht!)