First, you calculate the total amount of parts : 2 + 5 = 7
Next, divide the number by the total amount of parts : 28 ÷ 7 = 4
After that, you multiply the answer by the amount of parts needed on both sides of the ratio : 4 × 2 = 8 and 4 × 5 = 20
Finally put these answers back into the ratio : 8:20
So there are 8 students in the play
To check, make sure both sides of the ratio add up to the original number : 8 + 20 = 28