1 van can hold 9 students. Total are 31 students. So to find how many vans will be needed to fit these 31 students we will divide 31 by 9. Whatever is our answer will be the amount of vans. Lets do it:-
31 ÷ 9 = 3.44444.........
Since we cant take 3.44444....... vans we will round to 4 vans. There will be extra seats but all the students will fit.
So, to fit 31 students we will need 4 vans.
Hope I helped ya!!