GMAT CR Practical Thinking Examples

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Question Text Analysis

In Colorado subalpine meadows, nonnative dandelions co-occur with a native flower, the larkspur. Bumblebees visit both species, creating the potential for interactions between the two species with respect to pollination. In a recent study, researchers selected 16 plots containing both species; all dandelions were removed from eight plots; the remaining eight control plots were left undisturbed. The control plots yielded significantly more larkspur seeds than the dandelion-free plots, leading the researchers to conclude that the presence of dandelions facilitates pollination (and hence seed production) in the native species by attracting more pollinators to the mixed plots.

Text Analysis Approach:

1. First, look at the question type: It’s a “weaken” question. Then, analyze the passage structure to predict possible weakening directions.
2. First sentence: Usually provides background or definitions. Understand it as “two types of flowers coexisting.” The specific names dandelion and larkspur aren’t very important.
3. Second sentence: Understand it as “bees pollinate both species of plants.” This sentence doesn’t offer many predictable test points.
4. Third sentence: The test point is “experimental study,” so a possible weakening point is “sampling bias,” meaning questioning whether the sample is representative.
5. Fourth sentence: The samples are the two plants mentioned above. If a third plant appears later, it might be an irrelevant option.
6. Fifth sentence: The description mentions “experimental group vs. control group,” so a possible weakening point is “alternative cause,” meaning there’s more than one difference (variable) between the two sample groups.
7. Conclusion sentence: It’s a “cause-and-effect” type of statement. Based on the previous analysis, the most likely weakening direction is “alternative cause.”
8. Conclusion details: The conclusion involves a “comparison.” Pay attention to the comparison criteria: “number of larkspur seeds” and “pollination (seed production).” This will be key to determining the relevance of options.
9. Simplify the conclusion: Condense the conclusion into a question: “Do dandelions facilitate pollination (and seed production) by attracting pollinators?”

Solution Strategy Prediction

Which of the following, if true, most seriously undermines the researchers’ reasoning?

Predicted Correct Weakening Directions:

• Reversing cause and effect
• Alternative cause (finding other variables between the two sample groups)
• Sampling Bias (unrepresentative samples)

Predicted Irrelevant Directions:

• Introduction of a third plant species other than the two mentioned.
• Introduction of comparison criteria other than those in the conclusion.
• Only one side of the comparison is mentioned, without the other. (Similar to a DS question where only one condition is given, making comparison impossible)

Option Analysis

• (A) Bumblebees preferentially visit dandelions over larkspurs in mixed plots. Analysis: This option only discusses mixed plots (the group with both plant species) but doesn’t mention the group with only one species. We cannot determine the difference between the two groups. Eliminate.
• (B) In mixed plots, pollinators can transfer pollen from one species to another to augment seed production. Analysis: This option only discusses mixed plots (the group with both plant species) but doesn’t mention the group with only one species. We cannot determine the difference between the two groups. Eliminate.
• (C) If left unchecked, nonnative species like dandelions quickly crowd out native species. Analysis: The conclusion of the question discusses “seed production,” while this option talks about crowding out “plant numbers.” This goes beyond the conclusion’s comparison criteria, making the scope of discussion irrelevant. Eliminate.
• (D) Seed germination is a more reliable measure of a species’ fitness than seed production. Analysis: This introduces comparison criteria other than those in the conclusion, making the scope of discussion irrelevant. Eliminate.
• (E) Soil disturbances can result in fewer blooms, and hence lower seed production. Analysis: This points out an “alternative cause.” It suggests that the factor affecting seed count might be “soil” rather than “attracting pollinators” as stated in the conclusion. This matches our prediction, so it is correct.