$$\frac{2}{5}+\frac{1}{5}=\frac{2+1}{5}=\frac{3}{5}$$  

$$\frac{2}{5}+\frac{1}{5}=\frac{2+1}{5+5}=\frac{3}{10}$$  

$$\frac{2}{5}+\frac{1}{5}=\frac{1}{5+5}=\frac{1}{10}$$  

$$\frac{2}{3}+\frac{4}{5}=\frac{2}{3}+\frac{4}{3}=\frac{6}{3}=2$$  

$$\frac{2}{3}+\frac{4}{5}=\frac{2+4}{3+5}=\frac{6}{8}=\frac{3}{4}$$  

$$\frac{2}{3}+\frac{4}{5}=\frac{10}{15}+\frac{12}{15}=\frac{22}{15}$$  

$$\frac{3}{4}-\frac{2}{7}=\frac{3-2}{7-4}=\frac{1}{3}$$  

$$\frac{3}{4}-\frac{2}{7}=\frac{21}{28}-\frac{8}{28}=\frac{13}{28}$$  

$$\frac{3}{4}-\frac{2}{7}=\frac{3}{4}-\frac{2}{4}=\frac{1}{4}$$  

$$\frac{1}{2}+\frac{1}{3}=\frac{3}{6}+\frac{2}{6}=\frac{5}{6}$$  

$$\frac{1}{2}+\frac{1}{3}=\frac{1+1}{2+3}=\frac{2}{5}$$  

$$\frac{1}{2}+\frac{1}{3}=\frac{1}{2+3}=\frac{1}{5}$$  

$$\frac{63}{54}$$  

$$\frac{30}{54}$$  

$$\frac{33}{54}$$  

$$\frac{2}{3}$$  

$$\frac{4}{3}$$  

$$\frac{46}{40}$$  

$$\frac{24}{40}$$  

$$\frac{26}{40}$$  

$$y\ =\ \frac{5}{6}\ -\ \frac{4}{3}$$  

$$y\ =\ \frac{4}{3}\ -\ \frac{5}{6}$$  

$$y\ =\ \frac{5}{6}\ +\ \frac{4}{3}$$  

$$y\ =\ \frac{4}{3}\ +\ \frac{5}{6}$$