Q24 - A birth is more likely

[bbirdwell]

A No clue how the answers for 17 and 20 are what they are, and I don't know why the better answer for 23 is not E and the better answer for 24 is not A. Please help me out here

The conclusion:
There must be more ambidextrous people born to women over 40 than to younger women.

Premises:
Women over 40, more likely difficult birth
More difficult birth, more likely ambidextrous
Other causes of ambidexterity not related to mother's age.

What's strange about this? A conclusion about numbers of children is drawn based on various likelihoods. This is a logical no-no. Our answer should say something about the actual numbers of ambidextrous children.

(A) says that it's a circular argument. But it's not. Here's an example of an argument where this would be the correct answer: Money is the root of all evil, because evil can always be traced back to money.

This argument does not assume it's conclusion. It provides a few facts, and then states the conclusion.

(C)(D) and (E) don't matter at all.

(B) is the only choice that speaks to the core of the argument. Think about it. If it's true that fewer children are born to women over 40, then the conclusion loses a lot of strength. We know that these women are more likely to have an ambidextrous child, but if these women account for only a small % of all births, then we cannot definitely conclude that MORE ambidextrous children are born to them than to women under 40. It's still possible, of course, but much, much less certain.

[lrt1337]

I now understand why B is the correct answer through process of elimination, but I don't understand how the fewer children being born to women over 40 matters, particularly because there could still be objectively more ambidexterous children born to these women. Why does that affect the conclusion at all? Please help me understand this!

[john.as.camacho]

Hey, can someone please answer the above question about how B impacts the core of the argument.

Also, I don't think that there is a sufficient explanation for eliminating the other answer choices.

[maryadkins]

Yes, there still COULD be more ambi children born to these women but the conclusion is that there MUST be. This is what we're trying to weaken. And if there are fewer children born to women over 40, then that certainly attacks the conclusion that must be more ambi children being born to them. If 10 children are born to women under 40 and 5 are born to women over 40, even if 3 out of 5 in the over-40 crowd are ambi, we can have 4 out of 10 in the under-40 crowd that are ambi that while that's a lower proportion (40% versus 60%), it's still an overall bigger number (4 versus 3).

As for the other answer choices:

As Brian noted, (A) is a way of describing "circular logic" which you'll see as an answer choice on the LSAT sometimes. To make a general statement...this is rarely the correct answer. Circular logic, or setting out to prove what you've either stated or assumed, is going to be kind of obvious b/c it's going to look really weird as an argument. Like, "That's a towel because it's a towel" kind of thing.

(C) isn't needed—we don't need to know the numbers of the whole population. We just need to know comparative numbers for children of women over and under 40.

(D) makes WHEN a kid's handedness can be diagnosed an issue, but that's not an issue here.

(E) doesn't actually matter because we're already told that being over 40 makes it more like your birth will be difficult, and that THAT makes it more likely that your kid will be ambidextrous. We don't need to worry about HOW this happens.

Hope this helps clear things up!