# Making the big inference in a logic game

#### rick81

##### Making the big inference in a logic game
« on: January 27, 2005, 05:22:57 PM »
Hey folks,

Just a quick one.

Making the big inference in a logic game tends to be hit or miss with me - when I get - I generally get through the game very quickly, but when I don't - I struggle.

So my question:
What is the best way to improve/ensure that you make the big inference in a game? Do you look over the rules after you have diagrammed them? Do you diagram as you read? Or is this something that comes with practice?

Thanks,

PS - do you do the LG over and over again until you get the inference?

#### InVinoVeritas

• 5477
• Fine! I shall also fix zee hobo suit!
##### Re: Making the big inference in a logic game
« Reply #1 on: January 27, 2005, 05:30:22 PM »
I tended to look at the most restricted variable.  also, sometimes it helped to keep in mind which variable(s) can go anywhere.

here's my little piece of advice: take a game and do it untimed.  spend as much time as you need looking for that big inference.  as you do this with more and more games, you might find that finding the big inference gets easier.  (that was my experience, anyway.)

#### mattb23

##### Re: Making the big inference in a logic game
« Reply #2 on: January 27, 2005, 07:20:08 PM »
I think that the response above gives good advice in suggesting that you do some of the games without the time limit--but as you get even reasonably close to your test date, you'll want to practice under real conditions. Here are some of my own suggestions, based on what's worked for me (these are pretty general, if there's a specific game type that you have particular trouble with, let me know and I'll try and offer more specific suggestions). Sorry in advance if these are kinda rambling and use overly-simplistic examples, I'm better at doing this stuff than trying to explain it.

1. In terms of basic method, the first thing you obviously want to do is identify the entities and action of the game. This sounds super obvious, because you clearly see pretty quickly that it's a sequencing action, matching action, etc. But taking a few seconds to really just preview the game in your mind can be worthwhile in deductions; I think this is particularly true in selection/distribtuion games where the two entities aren't of equal number (i.e. choosing five people for six spots, or the opposite, five people for six spots). Reminding yourself that you're always going to have an unfilled slot, or are always going to have an entity that won't be used, are deductions in and of themselves, and simple numbers deductions like that can go a long way. Being familiar with the entities also helps you keep track of them during the questions; you'll have a better sense of which entities you've already permanently placed and which ones are still in-flux.

2. What I like to do is quickly copy the rules over in shorthand one-by-one before I diagram. This offers the benefit of translating each rule into the notation you're most comfortable with and forces you to spend a few seconds considering the meaning of each rule. I like to read a rule, shorthand it and then go to the next rule, but I think it'd be just as effective to read all the rules and then shorthand all the rules.

This is also the stage where you'll want to derive contrapositives for any "if, then" statements and make note of the obvious spatial deductions if there are any (like A before B and B before C, so A before C).

3. The Diagram--this is everything, in my view. It's well worth your time to draw a good master sketch--don't worry about taking extra seconds, you'll easily save them when you get to the questions. If there's a particular game-type that you have trouble diagramming, let me know, and I can offer some specifics. But for all the games--I like to put the rules into the sketch one by one (as you can clearly tell, I'm a big fan of going over the rules a few times--it really helps you grasp everything that's going on in the game and saves time later).

I think that perhaps the most critical aspect of the diagram is including not only what you know to be true but also what you know not to be true, even if it's not explicity stated in the rules. Say you're putting items A,B,C,D into four slots and the rules tell you that A comes before B and A comes before C. So obviously A can't be in the third or fourth slot. My apologies for the overly simplistic example, but marking the "nots" are huge--like if you're distributing people into three groups and Henry is in Group A, and the rules say Bob is never with Henry--be sure to mark that Bob isn't in A (which in turn means that Bob would have to be either in B or C, assuming that all the people have to be chosen; this is a prime example of the notion of dual options which I'll discuss below). Often times, you'll be able to figure out where a particular entity goes by eliminating all of the other places it could have gone.

I'd write your master diagram in highlighter pen and then use pencil for each of the questions. For some games, particularly matching, I'd just use the one diagram--for others, usually sequencing, I'd end up with 4 or 5. But if you feel good about your master diagram, try to keep using it both to save time and prevent against any errors in copying it over.

4. Dual Options--big, big concept that can turn some seemingly difficult games into a breeze. When reviewing the rules, try to bear in mind whether the situation is such that there are only two ways a game can play out. Sometimes that info is obvious and right in the rules (A is either in spot 1 or spot 6). If you get that kind of rule, draw two diagrams--once you've filled in the rest of the rules and made some smaller deductions, you'll have accounted for all of the game's possible outcomes in two sketches.

A slightly more drawn out example (though too simple--sorry, it's just easier for me to describe the concept with the ridiculous examples). Say you have entities A, B, C, D, E, F and G which must be placed in one of two groups--and you get a rule something like "A is grouped with at most two other entities" and another rule along the lines of "Each of the two groups has at least two entities." Those two rules give you a major numbers deduction--A has to be with one other entity, but can't be with more than two, so A's group has got to have either 2 or 3 of the entities and, correspondingly the other group has 5 or 4. You can then draw those two scenrios and have all the outcomes accounted for in the diagram--you can then breeze through the "Must be True" and "Can be True" questions.

5. Trust yourself, especially at the start of the game--if you've really thought through all the rules and have a great diagram and you don't see a "big" deduction, it might be because there isn't one--not every game will have a huge one that solves the game in and of itself. Always be aware of possible numbers-based deductions like the one I mentioned right above--it might not always be dual options, but the key deduction can often surround the sizes of certain entity groups.

If you still aren't seeing anything big, go to the questions. Often you'll find that if there wasn't a huge deducton, it's because the questions are really basic; and answering questions can help you find deductions you might have missed. Each time you find a viable game scenario in the answer choices, mark it with some different kind of color--if you can get one or two of these, then you've got some additional data to help with the "Could be True"  and "Must Be True" questions.

6.Overall, just keep on doing games. If you have a game you can't initially solve, study the explanation, wait awhile, and then go back to that game and see if you can see the key deduction then. Doing this will get you familiar with all of the speficic deduction types and increase your ability to spot them quickly.

I hope that this is somewhat helpful and please feel free to email me if I can be of further help.

#### shaz

• 1636
• University of Toledo Class of 2009
##### Re: Making the big inference in a logic game
« Reply #3 on: January 27, 2005, 09:44:25 PM »
Wow, how long did it take you to type all that?

#### mattb23

##### Re: Making the big inference in a logic game
« Reply #4 on: January 27, 2005, 09:47:09 PM »
Wow, how long did it take you to type all that?

Haha it didn't actually take too long. I'm in the final week of a fairly lengthy process of moving and shifting jobs, and really just sitting around in my parents' house all day doing nothing--so I gotta throw myself into something

#### rick81

##### Re: Making the big inference in a logic game
« Reply #5 on: January 28, 2005, 07:09:25 AM »
thanks a lot,
that was brilliant.

One last question - do you redo games? I find when I redo a game - I do quite well, but I am not sure if this is a plausible technique to attack the games.

Thanks for the great post.

#### mattb23

##### Re: Making the big inference in a logic game
« Reply #6 on: January 28, 2005, 11:08:15 AM »
thanks a lot,
that was brilliant.

One last question - do you redo games? I find when I redo a game - I do quite well, but I am not sure if this is a plausible technique to attack the games.

Thanks for the great post.

Glad it was helpful. Basically, I think the extent to which you redo games should be based on how much time you have. As noted in my post above, I think that whenever a game really gives you problems in terms of setting it up and seeing the deductions, that you're best served by reviewing the explanation, putting the game away for awhile, and then try it again a little later on to make sure you can then see the deduction yourself (but if I were you I wouldn't redo these games as part of any scored practice, as it'll misleadingly inflate your score).

I think that as far as logic games go, repetition is golden. So if you have the time and inclination to redo even the games you did well with originally, I'd say go for it--it can only help to improve your general speed. But clearly, don't redo games that you initially breezed through at the expense of ones you haven't seen yet.

Good luck.

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##### Re: Making the big inference in a logic game
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