so i’m not sure if there is a different way to do this but here’s how i did it:
start with 2:5
then just keep going up till you can add both numbers and get 28
so next i multiplied both sides by 2 to keep the ratio and got 4:10
then i went back and tried again and tried multiplying 3
which is 6:15.
that only is 21 students so it’s not right
next i tried 4
2 x 4 = 8
and
5 x 4 = 20
8:20 is still a 2:5 ratio and
8 + 20 = 28
so 8 students were in the teachers play
let me know if i can clarify anything