1. The problem states that the ratio of boys to girls is 1:3. 2. This means for every 1 boy, there are 3 girls. 3. To find the percentage of girls, first find the total parts: $1 + 3 = 4$ parts. 4. The fraction of girls is $\frac{3}{4}$. 5. Convert this fraction to a percentage by multiplying by 100: $$\frac{3}{4} \times 100 = 75\%$$. 6. Therefore, the percentage of girls is 75%, not 45%.