Logic Games Strategy Guide pg 175, #4

[hyewonkim89]

For the 3D Ordering setup, I'm confused about #4.

I drew the diagram right for everything else, but I don't understand why there are two 60's before 30 and after 60 (which is immediately after 30).

Please advise.

Thanks!

[ohthatpatrick]

This is a confusing inference, no doubt.

The 3rd rule of setup #4 is that each 30 minute is immediately followed by a 60 minute.

We could diagram that conditionally as:
30 --> 60 immediately after

The last rule tells us that the 4th spot will be 30 minutes.

__ __ __ 30 __ __

According to this rule, we have to put a 60 immediately after that 30.

__ __ __ 30 60 __

But, we don't want to stop there. We want to think about if there are any spots where we could NOT put a 30, because there would be no way to follow the rule.

Could we put a 30 in spot 1? Sure, that would force us to put a 60 in spot 2, which seems fine.

Could we put a 30 in spot 2? Sure, that would force us to put a 60 in spot 3, which seems fine.

Could we put a 30 in spot 3? No. That would force us to put a 60 in spot 4, which we can't do.

Since we can't put a 30 in spot 3, we must put a 60 in spot 3.

__ __ 60 30 60 __

Could we put a 30 in spot 6? No. That would force us to put a 60 in spot 7, but there is no spot 7.

Since we can't put a 30 in spot 6, we must put a 60 in spot 6.

__ __ 60 30 60 60

Let me know if you still have any questions about this.