Step-by-step explanation:
The number of total students is 18+12+10=40
So
1) 18:40 but simplified it will be 9:20
2) 10:40 but simplified it will be 1:4
3) 30:40 but simplified it will be 3:4
4) 30:10 but simplified it will be 3
5) 18:22 but simplified it will be 9:11
N.B simplified means dividing them by their common multiple. so the final answer for each is the number after it is simplified
