Answer:
1:5
Explanation:
Every student who brings lunch to school, there are 5 students who eat the school lunch; 1:5 would be the answer, because of the wording in the question. "Every student who brings lunch to school" meaning 1, and " 5 students who eat the school lunch" meaning 5 people who don't bring their own lunch. So eventually it will bring down to 1:5 as the ratio.
I hope this helped, sorry it repeats alot -.-