The ratio of girls to boys in Mr. Smith's homeroom is 3:4. The ratio in Mr. Smith's homeroom to students in the whole 7th grade is 1:5. The ratio of students in 7th grade to students in the whole middle school is 2:7. If there are 12 girls in Mr. Smith's homeroom, how many students are in the whole middle school?

3:4 = G:B

1:5 = Mr. Smith's class: 7th Grade

2:7 = 7th: Middle school

12 girls = 3 units

1 unit = 12/3 = 4

Boys = 4x4 = 16

Whole class = 28 students

Class : Grade = 1:5 7 = number of units in Mr. Smith's class

28 = 1 unit

5 units = 28x5 = 140 There are 140 kids in the grade

140 = 2 units

1 unit = 140/2 = 70

70x7=490

There are 490 students in the whole grade