[tex]\dfrac{1}{4}+\dfrac{3}{8}=(*)\\Find\ LCD\ (Least\ Common\ Denominator)\\list\ the\ multiples\\of\ 4:\ \ 0;\ 4;\ \fbox8;\ 12;...\\of\ 8:\ \ 0;\ \fbox8;\ 16;\ 24;\ ...\\LCD\left(\dfrac{1}{4};\ \dfrac{3}{8}\right)=8\\\\(*)=\dfrac{1\cdot2}{4\cdot2}+\dfrac{3}{8}=\dfrac{2}{8}+\dfrac{3}{8}=\dfrac{2+3}{8}=\dfrac{5}{8}[/tex]