Make sure the denominators (thats the bottom number) are the same!! This is very important!! For example, if you are subtracting 3/10 from 1/2 you are going to multiply 1/2 by 5 (because 2×5 is 10) and get 5/10. Now, what you are going to do is subtract 4 from 5 and get 1/10. I hope this helped!
The percent of boys in the class is 40% because 16 + 24 = 40 (the entire amount of kids) 16 / 40 = .4 then move decimal twice to the right for percentage which gives you 40%