Read the following table:
| Blood Group | Number of Students |
| A | 9 |
| B | 6 |
| O | 12 |
| AB | 3 |
| Total | 30 |
What is the ratio of the most common and rarest blood groups?
1
1 ∶ 4
2
1 ∶ 3
3
4 ∶ 1
4
3 ∶ 1
Read the following table:
| Blood Group | Number of Students |
| A | 9 |
| B | 6 |
| O | 12 |
| AB | 3 |
| Total | 30 |