Applicare la formula: $a+b$$=a+b$, dove $a=\frac{1}{2}$, $b=\frac{2}{5}$ e $a+b=0.5+0.4-\frac{2}{5}$

Applicare la formula: $\frac{a}{b}+c$$=\frac{a+cb}{b}$, dove $a/b+c=0.9-\frac{2}{5}$, $a=-2$, $b=5$, $c=\frac{9}{10}$ e $a/b=-\frac{2}{5}$

Applicare la formula: $ab$$=ab$, dove $ab=0.9\cdot 5$, $a=\frac{9}{10}$ e $b=5$

Applicare la formula: $a+b$$=a+b$, dove $a=\frac{9}{2}$, $b=-2$ e $a+b=-2+4.5$

Applicare la formula: $\frac{a}{b}$$=\frac{a}{b}$, dove $a=\frac{5}{2}$, $b=5$ e $a/b=\frac{2.5}{5}$