Since i do not know the amount of people in the school I will tell you another thing.
Every 50 students that are surveyed 10 are going to the game and 40 are not so 10/50 are going to the game or 1 in 5 students will go to the game (1/5)
So take the amount of people in the school and do this -
Say there are 200 that would be 40 people going to the game because
200 / 50 = 4 that would be 4 surveys (that would be 10 people from each survey going to the game) So, 4 x 10 (10 from each survey) Would be 40 people so use this to find you're answer I hope it helps you.
Start by dividing the total people in the school by 50 and for whatever number you get multiply it by 10.