\[\begin{array}{l}
1/3 + 1/4 + 1/5 + 8/10 + 15/20 + 20/30\\
= \frac{1}{3} + \frac{1}{4} + \frac{1}{5} + \frac{4}{5} + \frac{3}{4} + \frac{2}{3}\\
= (\frac{1}{3} + \frac{2}{3}) + (\frac{1}{4} + \frac{3}{4}) + (\frac{1}{5} + \frac{4}{5})\\
= 1 + 1 + 1\\
= 3
\end{array}\]

1/3+1/4+1/5+8/10+15/20+20/30
=(1/3+20/30)+(1/5+8/10)+(1/4+15/20)

=1+1+1=3

$\frac{1}{3}$ + $\frac{1}{4}$ + $\frac{1}{5}$ + $\frac{8}{10}$ + $\frac{15}{20}$ + $\frac{20}{30}$

= ( $\frac{1}{3}$ + $\frac{20}{30}$ ) + ( $\frac{1}{5}$ + $\frac{8}{10}$ ) + ( $\frac{1}{4}$ + $\frac{15}{20}$ )

= 1 + 1 + 1 = 3