To determine which two grades have a proportional relationship between the numbers of girls and boys, we need to compare the ratios of girls to boys for each grade.
Let's look at the given data and compute the ratio of girls to boys for each grade:
1. Grade 6
- Girls: 9
- Boys: 12
- Ratio: [tex]\( \frac{9}{12} = \frac{3}{4} \)[/tex] or 0.75
2. Grade 7
- Girls: 12
- Boys: 18
- Ratio: [tex]\( \frac{12}{18} = \frac{2}{3} \)[/tex] or approximately 0.667
3. Grade 8
- Girls: 15
- Boys: 20
- Ratio: [tex]\( \frac{15}{20} = \frac{3}{4} \)[/tex] or 0.75
4. Grade 9
- Girls: 25
- Boys: 36
- Ratio: [tex]\( \frac{25}{36} = \)[/tex] approximately 0.694
Now, we compare the ratios:
- Grade 6: 0.75
- Grade 7: 0.667
- Grade 8: 0.75
- Grade 9: 0.694
We see that Grades 6 and 8 both have the same ratio of 0.75. Therefore, the relationship between the numbers of girls and boys is proportional in Grades 6 and 8.
So, the two grades that have a proportional relationship between the numbers of girls and boys are:
6 and 8