Step 1: Let the total number of students be \( 10x \) and the total number of teachers be \( x \).
The number of boy students is:
\[ \frac{2}{5} \times 10x = 4x \]
The number of girl students is:
\[ \frac{3}{5} \times 10x = 6x \]
The number of male teachers is:
\[ \frac{4}{9} \times x = \frac{4x}{9} \]
The number of female teachers is:
\[ \frac{5}{9} \times x = \frac{5x}{9} \]
Step 2: The ratio of the number of boy students to the number of male teachers is:
\[ \frac{4x}{\frac{4x}{9}} = 9:1 \]
Conclusion: The required ratio is 9:1.