Question: Jabberwocky

Answer choice B suggests that it might be useful to know what fraction (or percentage) of all jimmylegs sufferers are LONGHAIRED jabberwockies.
For example, out of 100 jimmylegs sufferers perhaps 20 are longhaired. Or perhaps 30 are longhaired. etc.

It really comes down to the argument's conclusion. The author says that LONGHAIRED jabberwockies are NOT predisposed to getting jimmylegs. This conclusion is based on the fact that more SHORTHAIRED jabberwockies contract jimmylegs.

The main problem with the author's conclusion is that, in order to determine whether LONGHAIRED jabberwockies are predisposed to getting jimmylegs, we need to know the RATE at which LONGHAIRED jabberwockies get jimmylegs. We then need to compare this with the RATE at which NON-LONGHAIRED jabberwockies get jimmylegs.

So, it doesn't matter how many varieties of NON-LONGHAIRED jabberwockies there are.

Does that help?

Cheers,
Brent
PS: I'd say this question is in the 600-650 difficulty range

Question link: https://gmatclub.com/forum/a-neuron-needs-to-travel-to-the-place-in-the-...

I'm not a big fan of this question, but here goes my solution:

When it come to Cause and Effect arguments (e.g., Event A causes Event B), we should watch out for the possibility that the causation goes in REVERSE (i.e., Event B causes Event A)

The passage tells us that gene mutations can cause areas of faulty neurons and these areas can cause disorders.

If we negate answer choice A, we get: A disorder in a person DOES affect the mutations in the genes in that person.
This suggests that the order of cause and effect goes in reverse, which seriously undermines the argument.

Cheers,
Brent
Aside: I suggest you stick with official Critical Reasoning questions. They best represent what you'll see on test day.
You can use GMAT Club's question filter (https://gmatclub.com/forum/search.php?view=search_tags) to isolate tons of Official questions.