Official Solution:
More than 200 volunteers tasted two cola samples prepared from the same recipe. Only one sample had a small amount of white vinegar added. Before tasting, every volunteer was told, “One of these two colas contains a secret ingredient that makes cola taste better.” After sampling both drinks, a significant majority said the vinegar sample tasted better. Since white vinegar is not ordinarily viewed as a desirable cola additive, the researchers concluded that the expectation created by the announcement caused participants to perceive the vinegar cola as tastier.
Which of the following is an assumption the researchers must make in order to justify their conclusion?
A. None of the volunteers ordinarily prefers the taste of cola mixed with white vinegar.
B. The amount of vinegar added was too small for volunteers to detect by smell alone.
C. Volunteers believed that whichever cola tasted better probably contained the secret ingredient.
D. The vinegar sample and the non-vinegar sample were served at the same temperature.
E. The announcement did not make any volunteer feel pressured to agree with the researchers.
Premise 1: Every volunteer was told, “One of these two colas contains a secret ingredient that makes cola taste better.”
Premise 2: The only real difference between the two samples was that one had a small amount of white vinegar added, yet a clear majority judged that vinegar sample to be the tastier one.
Conclusion: The expectation created by the announcement—not any inherent appeal of vinegar—led participants to perceive the vinegar cola as better tasting; therefore, expectation influences experience.
A. CORRECT. None of the volunteers ordinarily prefers the taste of cola mixed with white vinegar.
If even a modest fraction of tasters already liked vinegar cola, their ordinary preference could fully explain the voting outcome, breaking the link from expectation to perceived taste. Because the argument collapses when this statement is false, it is a necessary assumption.
B. The amount of vinegar added was too small for volunteers to detect by smell alone.
Even if the vinegar were obvious by aroma, participants would still rely on expectation of a secret ingredient to judge which drink “should” taste better. Smell detection does not, by itself, undermine the causal chain, and frankly for the taste, they had to smell it, so this statement is not a required condition / assumption.
C. Volunteers believed that whichever cola tasted better probably contained the secret ingredient.
This almost an exact restatement of the premise - volunteers were told that the secret ingredient made the coal taste better and so this would be an inference of that statement and not an assumption. Expectation can bias perception even without consciously associating better taste with the secret ingredient. We don't need volunteers to believe anything.
D. The vinegar sample and the non-vinegar sample were served at the same temperature.
This is largely irrelevant as nothing in the argument talks about temperature and this therefore is not needed for the justification of conclusion. This factor is a potential weakener for the experiment, calling some of the results of the experiment into question but it is not a must have if there were slight differences of 1 degree for example The experiment would still work. An example of a required assumption would be: "The temperature difference between the two samples was not large enough to influence participants’ taste preferences.". Hopefully you can spot the difference with the "same temperature".
E. The announcement did not make any volunteer feel pressured to agree with the researchers.
Minor social pressure could influence which cola participants say is better, but the study’s claim centers on the psychological effect of expectation, not on conformity. The causal story still works even if some volunteers feel a bit of pressure.
Answer: A