Answer :
[tex]\frac{1}{4}+\frac{1}{7}\\\\LCD(\frac{1}{4};\frac{1}{7})=28\\\\\frac{1}{4}=\frac{7}{28};\ \frac{1}{7}=\frac{4}{28}\\\\\frac{1}{4}+\frac{1}{7}=\frac{7}{28}+\frac{4}{28}=\frac{11}{28}[/tex]
[tex] \frac{1}{4} + \frac{1}{7} = \frac{1\cdot7}{4\cdot7} + \frac{1\cdot4}{7\cdot4} = \frac{7+4}{28} = \frac{11}{28} [/tex]
