Challenge 35. I have a solution that works. It is not their solution. There answer doesn’t seem to work. Am I reading the instructions wrong. My solution includes a crossover piece.
The solution in the book for challenge 35 seems to be correct for me: A blue ball will be intercepted, if the register has an even value (0, 2, 4, 6) and a red one if the registers value is odd (1, 3, 5, 7).
The idea of the setup is to check the first bit only. If it’s a 0 we catch the blue ball, otherwise we flip it an trigger a red ball. This ball will be catched because of the flipped bit.
Although a crossover piece is not a allowed here for a correct solution, you should feel free to play around and experiment with other parts. Nevertheless the restriction of parts is part of the challenge 
I hope that helped. Feel free to share your solution.
All the challenges have more than one solution. If your solution works, be happy with that. You can always revisit it any try a different approach next time. Fewer parts etc. It is open-ended.
Thanks! I guess I figured that if they set the board up for the possibility for more numbers. Then they expected us to use them. I will keep this in mind if I find similar challenges in the future. Thanks again.
The solution in the book is not correct. For odd numbers the solution will be a blue ball, in contrast to the given task (odd -> red ball).
For the correct solution you need to use an orange crossover piece additional to the instruction given.
In the solution in the book it is impossible for any ball to reach bit 2 and bit 3 so that the register only is able to count 0 or 1
Sorry, the solution is correct. The Challenge is, to catch the ball with right color for preset numbers odd or even. But this is not soclearly formulated in the text, maybe because of the translation to German.
@Tatwie
We tried to manage counting while the tumble process, and then showing the right color for the result. But, the challenge starts after a preset number.