Section 3, Question 17 of the June 2007 LSAT is easy if you argue, and impossible if you don't. Let me show you what I mean: When exercising the muscles in one's back, it is important, in order to maintain a healthy back, to exercise the muscles on opposite sides of the spine equally.
Oh reeeeeeeeeallllllly?!?! You might be right about that, but you also might be completely full of shit. Maybe I like working out just one side of my back, and maybe my back is in perfect shape. What's your evidence for your assertion that I need to exercise both sides equally? Huh buddy? Let's hear it.
After all, balanced muscle development is needed to maintain a healthy back, since the muscles on opposite sides of the spine must pull equally in opposing directions to keep the back in proper alignment and protect the spine.
Yeah, well, I still don't believe you. What does "balanced muscle development" have to do with exercise? I mean, sure, it might be reasonable to think that working out affects muscle development. But "reasonable" doesn't cut it on the LSAT. I didn't see any evidence on that. Where's your proof that exercise affects muscle development? Your argument is incomplete until you can prove that point.
The question asks,
Which one of the following is an assumption required by the argument?
Through arguing, we've already answered this Necessary Assumption question. The argument has left something out: "Exercise affects muscle development." That's necessary because if exercise does NOT affect muscle development, then the argument can't possibly make any sense. We know exactly what we're looking for, before even looking at the answer choices. Piece of cake.
(A) Muscles on opposite sides of the spine that are equally well developed will be enough to keep the back in proper alignment.
We have a really strong prediction here, and this doesn't match that prediction. We don't even need to give it a second thought, unless we look at all five answers and don't find what we're looking for.
(B) Exercising the muscles on opposite sides of the spine unequally tends to lead to unbalanced muscle development.
Bingo. This answer bridges the critical gap between "exercise" and "muscle development." If this answer is untrue, it would ruin the logic of the argument. That means it's a Necessary Assumption of the argument, and is going to be our answer.
(C) Provided that one exercises the muscles on opposite sides of the spine equally, one will have a generally healthy back.
No way. The argument never said anything about "general health." This answer can't possibly be something that's required by the argument. Plus we've already found a perfect answer, in B.
(D) If the muscles on opposite sides of the spine are exercised unequally, one's back will be irreparably damaged.
This is wrong for the same reason as C. The argument never said anything about "irreparable damage." This answer can't possibly be something that's required by the argument.
(E) One should exercise daily to ensure that the muscles on opposite sides of the spine keep the back in proper alignment.
Same thing as C and D. The argument said nothing about "daily exercise."
Our answer is B, because it must be true or else the argument will fail. That's the definition of "Necessary." We're not always able to predict the answers so easily, but it's awful nice when it happens. Remember to slow down, in order to allow yourself to make the connections more frequently. You'll pick up time in the long run.