Atotal of 24 out of 40 sixth graders buy hot lunch each day. what percent of these students do not buy hot lunch each day?

60% of student don't buy a hot lunch. 
The simple way of doing it is by taking both numbers and dividing them.  24 divided by 40= 0.6  Since percents are part of a whole, we need to multiply by 100  0.6 times 100 equals 60.
Easy and accurate. 

24 out of 40 is 60%

So subtract 24 and 40
40 - 24 = 16

Now there is 16 out of 40 people that do not buy hot lunch

Now 16 out of 40 is 40%

So 40% of the students did not buy Hot Lunch, hope it helped