[tex]\frac{11}{13} <\frac{x}{15} <\frac{12}{13} \\\\\frac{11\times15}{13\times15} <\frac{13\times x}{13\times 15} <\frac{12 \times15}{13\times15}[/tex]
165<13x<180 |:13
[tex]\frac{165}{13}
Facem impartirea cu 2 zecimale si obtinem:
12,69<x<13,84
x ∈N ⇒ x=13
Deci fractia noastra va fi [tex]\frac{13}{15}[/tex]