班级里男生和女生的人数相等。女孩中的 $\frac{1}{2}$ 和男孩中的 $\frac{1}{4}$ 戴眼镜。求戴眼镜的学生人数与学生总人数的比。 答 : ___

1. Express the number of boys and girls using a common number of units.

Since the number of boys and girls are equal, and we need to find $\frac{1}{2}$ of the girls and $\frac{1}{4}$ of the boys, we can let the total number of girls be $4$ units and the total number of boys be $4$ units (using the common multiple of $2$ and $4$).
Total number of pupils = $4 + 4 = 8$ units.

2. Find the number of units for pupils who wore spectacles.

Girls who wore spectacles = $\frac{1}{2} \times 4 = 2$ units.
Boys who wore spectacles = $\frac{1}{4} \times 4 = 1$ unit.
Total pupils who wore spectacles = $2 + 1 = 3$ units.

3. Find the required ratio.

Ratio of pupils who wore spectacles to total pupils = $3 : 8$.