The problem is as follows:
A set of domino tiles is placed with one next to another as indicated in the diagram below. If the upper half of the next piece is labeled x and the lower half is labeled as y, then find x-y.
The choices given in my book are follows:
I found this riddle in my Reason and Logic book from the 2000s. From the style I believe it is adapted from a reprinted version of Martin Gardner's 50's book on Recreational Puzzles
I remember similar puzzles which asked for the least amount of domino pieces which need to be flipped vertically to make the count of pips on the upper and lower halves equal. My method of solving was to sum all the dots, divide this number by two, and see which tiles can be rotated in order to achieve equality.
But in this case I need to find some sort of logic to the ordering of the tiles (or at least I think so), and they appear to be in a random order, which confuses me.
I believe that this question (although it doesn't explicitly say) intends to imply that the set is a double-six. Hence it will have 28 tiles and 126 pieces.
So far I noticed that the third tile starting from the left is swapped upside down in the fourth place, right next to the double zero tile. This could mean that this domino comes from either the set of 3 or the set of 4. But again I couldn't spot anything other than that.
Can someone explain what kind of logic should be used to find the next term in this sequence? Is it just trial and error? I tried finding the difference between the pips in the upper and lower halves, but this didn't help much. Can someone please guide me to a solution? What strategy should be used?