The U.S. Department of Agriculture divides the North America : Critical Reasoning (CR)

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The U.S. Department of Agriculture divides the North America

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Intern

Joined: 13 May 2018

Posts: 6

Location: India

Schools: Darden '21 (S)

GMAT 1: 740 Q51 V39

GRE 1: Q170 V162

GPA: 3.5

Re: The U.S. Department of Agriculture divides the North America [#permalink]

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11 Jul 2018, 17:14

VeritasPrepKarishma
Hi Karishma and the gmatclub forum,

I have a couple doubts with this problem and would be great if somebody could resolve them. I agree why D could be the best possible answer. I actually got this one right but it took me quite a while to zero in on D. As I knew all the other answers were wrong, but there were a few sincere problems I had with D.

1) This doubt is extremely relevant to selecting the right option. Now as mentioned in the passage, "the correlation is strong", which the answer concludes, "There IS at least another factor in addition to or excluding average temperature". I don't see why this must be true. Why can't we have a different function with the same variable? For example, let's assume a variable for Average Temp = X, then the decision of the boundaries of Hardiness Zones is directly proportional to X. Why can't the second set of zones also just be a function of X. Length of trees = X^2 - 2X + e^X. Now both Types of zones are correlated but some of the trees in Type 1 might not be included in Type 2 due to a different relationship and/or different criteria in selecting the boundaries (different quantitative limits, for example)

2) I am aware that this piece of information is irrelevant to getting the right answer. Since "13 zones" is not mentioned explicitly (the only zones that are mentioned are Zone 1, 4, 6 and 13) whereas in the other type it is clearly mentioned that it has 11 zones. So, given a similar construction on the actual GMAT, are we supposed to assume that there are 13 zones. Now if one thinks it is only logical to assume zones in serial order, there are various real life examples with a discontinuity in labeling zones, one example, the area I live in doesn't have zone 3 and 5 but has a 1, 2, 4 and 6, since inception. In market demand analysis, zones are also denoted as Zone 1, 3, 9, 20, 34, etc, to compare the volume of demand among zones and to bring out the relevant heat factor in a heat map.

A reply would be greatly appreciated!!
Kudos to all!

Best,
Yohann

VeritasPrepKarishma wrote:

AmoyV wrote:

The U.S. Department of Agriculture divides the North American continent into “hardiness zones.” These zones are based on the average winter temperature and are used to determine what types of plants will likely survive in a given area. Zone 1 represents the coldest average winter temperature and zone 13 the warmest. The zones are closely correlated with, but do not exactly match another set of eleven zones that indicate the length of the growing season. Minneapolis is in hardiness zone 4 and Denver is in hardiness zone 6.

Which of the following statements is most supported by the information above?

A. During the coming winter, the lowest recorded temperature in Minneapolis will be lower than the lowest recorded temperature in Denver.
B. The growing season in Denver is much longer than the growing season in Minneapolis.
C. A greater variety of plants can be grown in Denver, due to the warmer average winter low.
D. Factors other than average winter temperature affect the length of the growing season.
E. At least one U.S. city has a colder average winter temperature than does Minneapolis.

Responding to a pm:
There is absolutely no ambiguity in this question.

Premises:
- Hardiness zones are based on the average winter temperature and are used to determine what types of plants will likely survive in a given area.
- Zone 1 represents the coldest average winter temperature and zone 13 the warmest.
- The zones are correlated with, but do not exactly match another set of eleven zones that indicate the length of the growing season - probably colder means shorter growing season from common knowledge
- Minneapolis is in hardiness zone 4 and Denver is in hardiness zone 6.

A. During the coming winter, the lowest recorded temperature in Minneapolis will be lower than the lowest recorded temperature in Denver.
We only know about average temperatures, not lowest.

B. The growing season in Denver is much longer than the growing season in Minneapolis.
Hardiness zones do not match the eleven "length of growing season" zone.

C. A greater variety of plants can be grown in Denver, due to the warmer average winter low.
No information about whether more variety survives in warm climate or cold - we will not use our general knowledge.

D. Factors other than average winter temperature affect the length of the growing season.
It is given that zones are correlated but DO NOT match exactly. It means other factors also come into play. Correct answer.

E. At least one U.S. city has a colder average winter temperature than does Minneapolis.
If you feel that "city" vs "area/town/piece of land" is nitpicking, then that's not correct. Perhaps a small wild piece of land right next to Canada lies in the hardiness zones 1, 2 and 3. Perhaps only some forest/mountain region lies in the first 3 zones. Perhaps no city lies in these zones since a city invariably ends up being warmer than the wild due to industrial activity. We don't know.
- But more importantly, North American continent includes not just US but also Canada and Mexico. Hence, even if you ignore the difference between city/town etc, nothing says that a US city must lie in first three zones. US and North America are not interchangeable!

Manager

Joined: 24 Sep 2018

Posts: 137

Re: The U.S. Department of Agriculture divides the North America [#permalink]

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13 Oct 2018, 10:45

Veritas Prep Official Solution:

Correct Answer is D.

This question illustrates a crucial logical principle: in order to show that an answer choice is incorrect on a “must be true” question, you do not need to show that it is “certainly not true”. All you have to do is come up with one example (which is often quite difficult) in which the conclusion is not true. On inference questions, it is unlikely that you will pick a “must be false” answer when you are asked for something that “must be true”. However, it is entirely possible that you will pick something that is likely to be true but not guaranteed to be true.

In this question, most of the incorrect answers are likely but not guaranteed. It is quite likely that, as choice A states, Minneapolis will have a lower extreme temperature than will Denver. Similarly, it is likely true that Denver has a much longer growing season. But neither is necessarily true. Denver has a higher average temperature, but that could be a result of shorter, colder winters and a quicker jump back to spring. And regarding choice B, the zones "do not exactly match" the length of the growing season, and Denver or Minneapolis might be one of those exceptions. Nothing states that the hardiness zones are associated with variety so choice C can be eliminated because of this fact.

For the most difficult incorrect answer - choice E - it seems that there must be a colder city since Minneapolis is only a four on a one to thirteen scale. However this scale is not just for cities and it is for all of North America, not just the U.S. It could very well be that the coldest city is a 4 (Minneapolis!) and only other rural areas or place outside of the U.S. are given lower ratings. D, however, can be proven: if the zones are not identical, then there must be another factor that accounts for the difference between hardiness zone and length of the growing season.
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