This is an explanation of the first logic game from Section III of LSAT Preptest 35, the October 2001 LSAT.
Four astronauts are needed for a space flight. There are eight candidates: four experienced astronauts – F, J, K, and L; and four inexperienced astronauts – M, N, P, and T. The group has four geologists (F, M, P, and T) and four radiobiologists (J, K, L, and N).
This is an in/out game. Many students find it difficult. I think it tests an incredibly important skill: how well and how quickly you can use a diagram.
This is actually a very simple game. We’ve got to pick four astronauts. Two are experienced, and two aren’t. Two of them need to be radiobiologists, and two have to be geologists. Lastly, either P or L or both have to be included.
Here’s my drawing that explains everything. Now, your first impression might be “huh?”, but give it a chance. It will let you solve everything very quickly:
It’s just a list of the experienced and inexperienced astronauts. I’ve put a box around those that are geographers. Those that are radiobiologists aren’t highlighted.
I’ve seen people use this vertically, or put another symbol around the radiobiologists, or make any number of stylistic changes. That’s fine. Draw it in a way that makes sense to you. But make sure you understand the logic. Here are the rules.
- You need two people from each row. (E/not E)
- You need two people with a box, and two people without a box.
- You need to include either P or L.
Study the diagram well. I’m going to reproduce it with each question.
The questions are mostly local rules. For instance, question two tells you that F and P are included. They both have a box, so they’re geologists. So look at your diagram: who else do you need?
You’ll need N (an inexperienced radiobiologist) and one of J/K/L (experienced radiobiologists.) That’s answer choice A. Done.
So the steps are:
- Check who the local rule selects.
- Look at the diagram, and count how many astronauts of each type that gives you.
- Figure out which other types you need to fill your quotas (experienced vs. inexperienced, R vs. G, do we have L or P?)
- Figure out which of the remaining astronauts therefore have to go, and who else could go. It won’t be very many.
- Check what the question is asking for, and choose the right answer.
- Score perfectly on this game!
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