N. 150

$\big(-2+\frac{4}{7}\big)+\big(-\frac{3}{7}+\frac{6}{14}\big)+\big(\frac{3}{2}-\frac{5}{14}\big)$=

=$\big(\frac{-14+4}{7}\big)+\big(-\frac{3}{7}+\frac{3}{7}\big)+\big(\frac{21-5}{14}\big)$=

=$-\frac{10}{7}+0+\frac{16}{14}$=

=$-\frac{10}{7}+\frac{8}{7}$=

=$-\frac{2}{7}$.

(-2+4/7)+(-3/7+6/14)+(3/2-5/14)

3/7 e 6/14 sono la stessa cosa

-10/7+(21-5)/14 = (-20+16)/14 = -2/7