Weighted average: total age ÷ total students.<br><br>
• Total age of boys = 15 × 12 = 180 years<br>
• Total age of girls = 10 × 11 = 110 years<br>
• Total age of class = 180 + 110 = 290 years<br>
• Total students = 15 + 10 = 25<br>
• Class average = 290 ÷ 25 = 11.6 years<br><br>
Final Answer: 11.6 years old