Q7 - A population of game ducks at a western lake

[syousif3]

I'm not sure how A is the right answer. I don't see how it can be inferred. I initially picked C and now I'm having a hard time seeing why A is the right answer.

[timmydoeslsat]

We are dealing with a must be true question stem.

We learn that the greater the sex disparity ratios, the greater the % of older male ducks in the population.

And we know that the eastern lake has a greater disparity than the the western lake: eastern (65-35 male majority) to western (55-45 male majority).

This means that it must be the case that the eastern has a greater % of older male ducks in the population.

Our correct answer says just that, albeit on the flip side, where the western has a lower % of older male ducks than the eastern.

[wzom10]

For what it's worth, here's my thought process. Hope it helps someone out... IN THE FUTURE

stim:
-Wst 55M:45F (not so great disparity, adult males might not outnumber adult females), Est 65M:35F (great disparity, greater pop of males)
-more M than F ducks
-only slightly more M than F in young
-way more M than F in older

conclusion:
greater disparity in gender ratio = greater percentage of older male ducks in population.

answers:
(A) looks good so far, come back.
(B) we're concerned with adult males, not all adult ducks; eliminate.
(C) good, come back.
(D) talks about hatching ducks, out of scope; eliminate.
(E) we're concerned with adult males, not females; eliminate.

(A) vs (C):

(A) talks about the percentage of male ducks, while (C) talks about "total number of males". We don't know anything about the actual # of ducks in either lake, we only know about the sex ratios, thus (A) is tighter match than (C). (A) states that the western lake contains a lower percentage of males than the eastern lake? can this be true? Stim says "Greater disparity in sex ratio = greater % of adult males". West has 55:45, east has 65:35. Therefore, west has a lower percentage and east has a higher percentage.


answer ---> (A).

[lissethbayona]

I understand why (A) is the right answer but I don't thoroughly understand why (B) is wrong.

I think (B) is not necessarily true because the stimulus only tells us that, "among those ducks that have not yet bred there are only slightly more males than females" and "there are appreciably more males among adult ducks than among young ducks." So with this information it is still possible for the percentage of young male ducks to be the same at both the western and eastern lakes while at the same time satisfying the ratios given in the first sentence.

Can anyone weigh in on this and let me know if I am close. Thanks!

[ohthatpatrick]

Yeah, you've got it.

We just can't prove much at all about "nonadult game ducks". Assuming "nonadult" allows us to infer "have not yet bred", the only thing we know about ducks who have not yet bred is that there will be slightly more males than females.

There's no way we can compare the western lake to the eastern lake. The only rule that lets us compare one lake to another is the last sentence, and that only allows us to infer a comparison about the % of older male ducks in the population.

If you want actual numbers to show the counterexample you had in mind, here you go.
Western Lake
55 males (20 nonadult, 35 adult)
45 females (19 nonadult, 24 adult)

Eastern Lake
65 males (20 nonadult, 45 adult)
35 females (19 nonadult, 14 adult)

(B) is talking about the % of nonadult ducks at each lake.

At Western lake, 39 of the 100, or 39% are nonadult.
At Eastern lake, 39 of the 100, or 39% are nonadult.

[bobbiejean.ajt]

For what it's worth, here's my thought process. Hope it helps someone out... IN THE FUTURE

stim:
-Wst 55M:45F (not so great disparity, adult males might not outnumber adult females), Est 65M:35F (great disparity, greater pop of males)
-more M than F ducks
-only slightly more M than F in young
-way more M than F in older

conclusion:
greater disparity in gender ratio = greater percentage of older male ducks in population.

answers:
(A) looks good so far, come back.
(B) we're concerned with adult males, not all adult ducks; eliminate.
(C) good, come back.
(D) talks about hatching ducks, out of scope; eliminate.
(E) we're concerned with adult males, not females; eliminate.

(A) vs (C):

(A) talks about the percentage of male ducks, while (C) talks about "total number of males". We don't know anything about the actual # of ducks in either lake, we only know about the sex ratios, thus (A) is tighter match than (C). (A) states that the western lake contains a lower percentage of males than the eastern lake? can this be true? Stim says "Greater disparity in sex ratio = greater % of adult males". West has 55:45, east has 65:35. Therefore, west has a lower percentage and east has a higher percentage.


answer ---> (A).

"We don't know anything about the actual # of ducks in either lake, we only know about the sex ratios,..."
This is the line i read that gave me the key to what i was missing. I initially chose A but when I saw C it appeared to be pretty cut and dry. The western lake clearly had more male game ducks, but then I read your quote. Only at that time did I see that I was missing the numbers were ratios and no exact count of the game ducks existed. The Western Lake could have over a 1000 game ducks and the Eastern lake only a few hundred and this would make C incorrect. It makes sense now.