[tex]\frac{1}{2}+\frac{1}{3}+\frac{1}{4}=\frac{6}{12}+\frac{4}{12}+\frac{3}{12}=\frac{13}{12}=1\frac{1}{12}\\\\\\ \frac{2}{5}+ \frac{3}{10}=\frac{4}{10 }+ \frac{3}{10}=\frac{7}{10}[/tex]
