\(\frac{7}{10}< \frac{15}{x}< \frac{7}{9}\)
\(\Rightarrow\frac{105}{150}< \frac{15}{7x}< \frac{105}{135}\)
\(\Rightarrow135< 7x< 150\)
\(\Rightarrow19< x< 21\)
\(\Rightarrow x=20\)
\(\frac{7}{10}< \frac{15}{ }< \frac{7}{9}\)
\(\Leftrightarrow\frac{7}{10}< \frac{15}{13}< \frac{7}{9}\)
Vậy chỗ cần tìm là 13 @@