Here's my solution: x=2233445566 y=7788990011 z=9988776655 6 * 6 = 36 (last digit stays the same) 1 * 1 = 1 (last digit stays the same) 5 * 5 = 25

Here's my solution: x=2233445566 y=7788990011 z=9988776655 6 * 6 = 36 (last digit stays the same) 1 * 1 = 1 (last digit stays the same) 5 * 5 = 25 (last digit stays the same) so: x^N ends with 6 y^N ends with 1 z^N ends with 5 for just that last digit, 6 + 1 != 5. qed