Which ratio is the odd one out?

10:40 or 5:20 or 1:4 or 3:12 or 8:33

10:40

This ratio is 10/40. Divide both by 10. You will get 1/4. 1/4 is 1:4.

So, we have one answer

1/4

5:20

This ratio 5/20. Divide both by 5. You'll get 1/4. 1/4 is 1:4

1:4

1:4 is the ratio we had before.

3:12

This ratio is 3/12. Divide both by 3. You'll get 1/4. 1/4 is 1:4

1:4

8:33

This ratio can not be reduced further.

So, the solution is 8:33 which has a different ratio from all the other ones