$\frac{9}{10}$ + $\frac{7}{9}$ + $\frac{5}{8}$ + $\frac{3}{7}$ + $\frac{3}{5}$ + $\frac{2}{5}$ + $\frac{4}{7}$ + $\frac{3}{8}$ + $\frac{2}{9}$ + $\frac{1}{10}$
= ($\frac{9}{10}$ + $\frac{1}{10}$) + ($\frac{7}{9}$ + $\frac{2}{9}$) + ($\frac{5}{8}$ + $\frac{3}{8}$) + ($\frac{3}{7}$ + $\frac{4}{7}$) + ($\frac{2}{5}$ + $\frac{3}{5}$)
= 1 + 1 + 1 + 1 + 1
= 5