Lesson 3 HW, Pg 3-47, Game 10

[rameday]

For game 10 on page 3-47 I am not sure how they got the answer to question 1 & 4. I understand that k/O have to be together but for example number 4 I thought the answer was E and for number 1 I had no idea how to go about answering that question.


A

[BethRibet]

Hi Rameday,

Thanks for posting.

K and O can not be together, they have to be next to each other, in either order. (KO/OK). So for question #1, that immediately rules out answer choice C. H and Z are also not together, because according to the first rule: H > Z. That rules out B. Since K and O need to be right next to each other (rule 3), and I has to be on Thursday (rule 2), we also can think about the overall sequence.


That is: __ __ __ _I_ __
M T W R F

Notice that with I on Thursday, the only way that K or O could be on Friday would be if Thursday has two people. But in the local role for #1, 2 people are on Tuesday. With 6 people fit into 5 days (and one per day except for one day with two students), only one day will have two people. That means only I can be on Thursday, so K and O must come before I in order to be placed together. K & O could go Monday or Tuesday, or Tuesday and Wednesday, to comply with the rule. Notice that either way, one of them will go on Tuesday (with the other on either Monday or Wednesday). Therefore we can rule out any answer choice that doesn't include either K or O on Tuesday. That is, the right answer choice can't have both K & O, but must have one of them. That makes it pretty clear, the only remaining answer is D.

For question #4:

We need to find a day which, if it includes Z, will fully determine the schedule. The only rule we have about Z is that Z comes some time after H. That is Z is not on Monday. So that rules out answer choice A.
You can check each remaining answer choice to see which one places U for sure. My instinct however is to start by checking what happens if Z is on Thursday, because putting Z with I on Thursday again will give us information about where K & O have to be.

__ __ __ Z+I __
M T W R F

Again, because K & O need to be next to one another (rule 2), we know neither can go on Friday, since Thursday is already full. We also know H precedes Z, based on rule 1, so it can't go on Friday. To make sure that one person is seen every day then, the only person left who can go on Friday is U. Therefore if Z is on Thursday, that determines that U is on Friday. So the correct answer choice is D.

Hope that helps!
Beth

[kim4956]

Can somebody explain to me how to arrive at the answer for question 3? Do we just have to plug in the answer choices? It seems pretty time-consuming, so I'm wondering if there's a quicker way to solve problems like this.

Also, I must be missing something, but when I tried plugging in some of the answer choices for this question, (D) wasn't the only possible answer. So I think I'm either missing an inference or did not carry out one of the rules...

Clarification appreciated!

[Adam Tyson]

Ah, the dreaded "5 if" question! Yes indeed, those can be a time consuming pain in the neck, and for that reason they may be good candidates for skipping and saving until the end of the game so that you can apply whatever you have learned from all the other questions.

That said, the approach is typically to do exactly what you thought, just test them all one at a time to see which one is right (although you may be able to eliminate some wrong answers quickly without testing just by looking at the rest of your work to see if you've already disproven them). However, in a question like this, where they are asking which one MUST be true, you don't want to test them by seeing if they COULD be true. Instead, see if you can violate them. For example, answer A - if U is on Monday, does H have to be Tuesday? Test it by putting H somewhere other than Tuesday (I tried it on Thursday, with I, forcing Z to Friday and the OK block fits in either order at Tuesday/Wednesday). If you can find a solution that violates the answer, then that answer does not have to be true, and is therefore a loser.

D is the right answer because once you place U on Thursday, there is no way for Z to go anywhere other than Friday. Try putting it somewhere else and you will find that either the OK block won't fit or else H is not before Z.

Again, test those Must Be True questions (whether or not they are of the "5 if" variety, with every answer starting with the word "if") by seeing if you can find an alternative. If you can, then it doesn't have to be true, but if you cannot find an alternative then it must be true and is the right answer.

I hope that helps!

[lauratenorio]

Couldn't you put Z in tuesday and wouldn't that have the same effect? the rules don't say you can't put two on tuesday

[Adam Tyson]

Which question are you referring to, lauratenorio? Yes, Tuesday can be the day that has two students scheduled, with every other day having just one student. If Z was on Tuesday, H would have to be on Monday. Then the OK block could be Tuesday and Wednesday, or Wednesday and Thursday, or Thursday and Friday. U would then take whichever day did not yet have something (Wednesday or Friday).