The ratio of the number of junior high students to the number of senior high students in a school is 7 to 9. If there are 100 more senior high students than junior high students, how many junior high students are there?

Answer 1

if there are n jr high students, then we have

n/(n+100) = 7/9
9n = 7(n+100)
2n = 700
n = 350