Explanation:

- Let the number of boys be x.

- Then, girls = x + 50% of x = x + 0.5x = 1.5x

- Total students = x + 1.5x = 2.5x

- Total age of boys = 12x

- Total age of girls = 11 × 1.5x = 16.5x

- Combined total age = 12x + 16.5x = 28.5x

- Average age = Total age / Total students = 28.5x / 2.5x = 11.4 years

- Option 2: 11.4 years is correct.

- Option 1 and 3, 4 are incorrect because the weighted average comes closest to the girls’ average but is more than that, not less or much higher.