Step-by-step explanation: There are 120 students, three-fourths are girls. Nine out of twelve is equal to three fourths, if you add a zero to the end of twelve and nine you get 90 out of 120, which is how many girls there are. If you subtract 90 from 120 you get 30 or one-fourth. The number of boys is equal to one-fourth because there is only one-foutlrth left. So, there are 30 boys.
