\ \ \ a=\frac{13}{26}\\\\\\\frac{6}{13}<\frac{13}{26}<\frac{7}{13}" alt="\displaystyle \tt \frac{6}{13}=\frac{12}{26}\\\\\frac{7}{13}=\frac{14}{26}\\\\\\\frac{12}{26}<a<\frac{14}{26} \ \ \ \ \ \ \ => \ \ \ a=\frac{13}{26}\\\\\\\frac{6}{13}<\frac{13}{26}<\frac{7}{13}" align="absmiddle" class="latex-formula">