Avi's pet hamster chubby loves to run in his hamster wheel. during one "race", avi counts 100 rotations of the wheel. she wants to know how far chubby ran, so she measures the diameter of the wheel and finds that it is 20 cm.

The first one, i believe, would be correct. all the others have one thing in common, and that's that they have repeating numbers. in the second one, x and y have repeating 6's and 3's, and in the third, x and y have repeating 6's as well. in the last one, there are repeating 3's. the first one has no repeating numbers.