Almost all of these pattern/sequence questions have a sequence that is either.
- Adding or Subtracting by a constant amount.
- Multiplying or Dividing by a constant amount.
We can easily check if it is case #1 by normalizing all the denominators with a least common multiple, like so.
7/18
6/18 (1/3)
5/18
4/18 (2/9)
From here the pattern seems rather clear, no? Seems to be a clear case of subtracting by a constant. (1/18)
If you want to do this faster next time, you could also note that there is a 7/18 that decreases to 5/18 in 2 steps, where you could probably guess this result, and then you could quickly check afterwards.

MATTHEW P.
06/11/19