by stacksdoe Sat May 09, 2015 10:49 am
Royaimani-
[color=#BF0080]To clear up some vocabulary: I use slot, space, goes,position all to mean the space on the line diagram that a variable can be placed.
Rina has it, but I'll piggy back off her: There are a few conditional inferences that can be produced during the initial set up and they completely make this game much easier then it seems. Rules two and four produce the following 4 inferences: (1) If X is $15 then Z is either $10 or $15, (2) If X is $12 then Z must be $10 (because as the rule states "lot X cost more than lot Z", (3) If Wednesday is $15 then Friday is either $12 or $15, (4) And lastly, if Wednesday is $12 then Friday must be $10.
As a side note: the numerical relationship/distribution (i.e. the amount of slots to variables ratio is unfixed, i.e. the variables can be placed in more then one space, except for X; with a little bit of analysis, it becomes apparent that X can only be placed once in all cases. Here is how this works, lets say parks in lot X two days, this would mean that she must park in lot Z three days, since she parks in lot Z on more days then in lot X, but this would leave no empty space for lot Y, consequently violating what is stated in the scenario, that "she parks in each of the three lots at least once".
The above four inferences do make # 20 easier, and it also helps gain a better understanding of the whole game and with other questions, especially # 22.
Back to # 20. Instead of going into depth in how to arrive at the correct answer, because Rina has done that, I'll just answer your question. The reason why Y can not be slotted for $15 is because that would force X to be $12 since Z is $10, but the question stem dictates that Z be $12, that's one reason. Additionally, if you attempt to slot Wednesday and Thursday with lot X for $15, you would already violate the last rule( that Z be slotted more days than X) because if X is slotted twice then Z would have to take up three days, thus leaving no empty slot for Y; and as we know, each lot has to be used " at least once".
While I was proof reading this I also noticed an error that is giving you a headache. If you slot Y for $15, then you must place Y on Thursday, because rule 1 states that "Thursday she parks in the $15 lot". And if you did this, you would still force X to be $12, which contradicts the question stem, "that lot Z be $12).
I hope this clears up a lot.
I have found the more inferences you can produce at the onset the better of you will be when attacking the questions. [/color]