Respuesta :
300:600 because 1/3x900=300 and 300 plus 600 equals 900 and simplified to simplest form it would be 1:2
if one third of the students bring their lunch the ratio would be 1:3 . 1:3 is equivalent to 3:9 which is equivalent to 300:900 therefore the ratio of students who bring their own lunch to students who don't bring their lunch is 300:900