Answer:
9:1, 18:2, 27:3, 36:4, 45:5 or 1,2,3,4,5
Explanation:
This is the answer because:
1) We can see that eah ratio is being multiplied with the next number. We can say this because 9 x 2 = 18 and 1 x 2 = 2 which is 18:2 just like that 9 x 3 = 27 and 1 x 3 = 3 which makes the ratio 27:3.
2) If we keep on doing this, 9 x 4 = 36 and 1 x 4 = 4 which makes the ratio 36:4.
Therefore, the answer is 4.
Hope this helps! :D