In a partially completed puzzle, I was faced with a row of 5 remaining possibilities: 1237, 1237, 237, 1239 and 179. Looking to find a matched pair in this, I reduced to 1237, 1237, 237, 19 and 19. This ultimately led to a correct solution.
Was this logic or guesswork, and if the latter, what were the mathematical possibilities of error?
Any help would be appreciated.