Seventy percent of the 100 students in middle school cafeteria bought their lunch sone of the students that brought there own lunch leave the cafeteria to attend a assembly now only 60% of the remaining students bought their lunch how many students are remaining in the cafeteria

So we solve for each
70% of 100=70
students who didn't buy lunch=100-70=30

some of the 70 left so that the students who bought lunch, are 60% of those who are left
we know that the students who didn't buy lunch didn't change number so therefor
100% of students left-60%=40%= students that didn't buy lunch=30 so
40%=30
20%=15
100%=75
there were 75 students lfet in the cafeteria

Do you need with the x value for the minimum? its always between the two intercepts for a parabola