Question 979640
7:9 is the ratio.

7/16 students are jr.

x=jr high
x+100=sr. high

x/x+100 = 7/9
cross-multiply
9x=7(x+100)
9x=7x+700
2x=700
x=350
x+100=450

800 students in all
350/450 =7/9, if one divides both numbers by 50.