Linear Setup Practice Drill #11, Rule 4

[Kelly JCU21]

The Setup diagram has a box that says Z_T
The rule says that --The driver picks up exactly one passenger between picking up T and Picking up Z.

This seems to me like it would be T_Z? This rule threw off the whole game for me, can someone please explain?

[Adam Tyson]

Thanks for the question, Kelly JCU21! The language of that rule actually tells us nothing about the order of those two variables, only that there is something between them. It's no accident that they gave us that rule the way they did - they are trying to get you to make that (incorrect) assumption! If they had meant that the variables had to be in that order, they would instead have said something like "The driver picks up exactly one passenger after picking up T and before picking up Z." Without those indications of specific order, though, either order is possible.

But wait, there's more!

The last rule tells us that Z has to be before T, fixing the order for us! It's for that reason that we have written the rule the way we did. Otherwise, without that rule to tell us the order, we would have written it to show that either order was acceptable, like so:

T/Z_Z/T

That means "either T_Z or else Z_T."

Don't assume the order is set by the order in which the variables are named - that's the kind of bad assumption the authors are testing to see if you will make (and be doomed!) or avoid (and crush the game).

Here's a similar situation you might encounter: "P and R arrive consecutively." That also tells us nothing about the order of P and R, as it could be PR or else RP. In both cases, they arrive consecutively. Sometimes they are kind and say "not necessarily in that order," but other times they leave you hanging, and you have to be careful to consider the options.

Keep at it, and good luck!