In an experiment, subjects were shown a series of images on a computer screen, appearing usually at the top but occasionally at the bottom. Subjects were asked to guess each time where the next image would appear on the screen. They guessed correctly less than half of the time. The subjects all reported that they based their guesses on patterns they believed they saw in the sequence. Instead, if they had simply guessed that the next image would always appear at the top, they would have been correct most of the time.

Summary
Images shown to subjects in an experiment usually showed up at the top of the screen but sometimes showed up at the bottom.
When asked to guess where the next image would appear, the subjects were correct less than half of the time.
Their guesses were based on patterns they thought they saw.
If they always guessed that the image would show up at the top, they would guess correctly most of the time.

Notable Valid Inferences
The images showed up at the top of the screen over 50% of the time.

A
If the subjects had always guessed that the next image would appear at the top, they would not have been basing their guesses on any pattern they believed they saw in the sequence.
Could be false. It could be that the strategy of always guessing that the images would be at the top came from repeatedly observing the image at the top. In the world where the subjects were always guessing top, we don’t have the information to say what this guess was based on.
B
Basing one’s guesses about what will happen next on the basis of patterns one believes one sees is less likely to lead to correct guesses than always guessing that what has happened before will happen next.
Could be false. (B) compares the strategy that the subjects used (basing guesses on perceived patterns) with a strategy that is not mentioned in the stimulus, so we cannot say which of these strategies is more likely to lead to correct guesses.
C
There was no predictable pattern that one could reasonably believe occurred in the series of images on the computer screen.
Could be false. It could be the case that there was a predictable pattern, but that the subjects didn’t pick up on it quickly enough to guess correctly a majority of the time.
D
Some of the subjects sometimes guessed that the next image would appear at the bottom of the computer screen, but were incorrect.
Must be true. Since subjects guessed correctly less than half of the time but would have been right most of the time by always choosing "top," they must have sometimes guessed "bottom" and been wrong. Otherwise, their accuracy wouldn’t be below 50%.
E
The most rational strategy for guessing correctly where the next image would appear would have been simply to always guess that the image would appear at the top.
Could be false. While we know that always guessing top would be more accurate than the strategy that the subjects used, we don’t know that always guessing top would be the most accurate strategy. There could have been other, more accurate, strategies.

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When a chain of service stations began applying a surcharge of $0.25 per purchase on fuel paid for by credit card, the chain’s owners found that this policy made their customers angry. So they decided instead to simply raise the price of fuel a compensatory amount and give a $0.25 discount to customers paying with cash. Customers were much happier with this policy.

Summary
A chain of service stations charged a $0.25 fee per purchase for fuel paid for with a credit card. This caused the service station’s customers to be angry. Instead, the chain decided to raise the overall price of fuel and offer customers a $0.25 discount for paying with cash. The service station’s customers were happier with this policy.

Strongly Supported Conclusions
Sometimes people’s reactions to a situation depends in part on how that situation is presented to them.

A
People usually adopt beliefs without carefully assessing the evidence for and against those beliefs.
This answer is unsupported. We don’t know from the stimulus under what circumstances people will usually adopt beliefs.
B
People’s perceptions of the fairness of a policy sometimes depend on whether that policy benefits them personally.
This answer is unsupported. We don’t know from the stimulus whether people think this policy is fair. We can’t infer from their happiness that they think it is fair.
C
People usually become emotional when considering financial issues.
This answer is unsupported. We don’t know from the stimulus under what circumstances people usually become emotional.
D
People often change their minds about issues that do not make significant differences to their lives.
This answer is unsupported. We don’t know from the stimulus under what circumstances people change their mind. We don’t even know if the customers who were previously angry are the same customers that are happier after the policy change.
E
People’s evaluations of a situation sometimes depend less on the situation itself than on how it is presented to them.
This answer is strongly supported. The only thing that changed in this scenario was whether or not customers were aware of the surcharge.

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Several Tyrannosaurus rex skeletons found in North America contain tooth marks that only a large carnivore could have made. At the time T. rex lived, it was the only large carnivore in North America. The tooth marks could have resulted only from combat or feeding. But such tooth marks would have been almost impossible to inflict on the skeleton of a live animal.

Summary

There are several T. Rex skeletons found in North America with tooth marks that could only have been made by a large carnivore. T. Rex were the only large carnivores in North America when they lived. The tooth marks could only have resulted from combat or feeding. These tooth marks would have been impossible to inflict on the skeleton of a live animal.

Strongly Supported Conclusions

The tooth marks on the T. Rex skeletons are likely a product of other T. Rex’s feeding on T. Rex bodies.

A
T. rex regularly engaged in combat with smaller carnivores.

This is unsupported because we don’t have information about tooth marks being found on the skeletons of other carnivores or any other evidence of such combat.

B
At the time T. rex lived, it was common for carnivores to feed on other carnivores.

This is unsupported because even though T. Rex appears to have fed on other T. Rex, we don’t know that this was common for other carnivores.

C
T. rex sometimes engaged in cannibalism.

This is strongly supported because we know that the marks on the skeletons could only have come from other T. Rex’s, and they could only have been made during feeding on an already dead animal.

D
T. rex sometimes engaged in intraspecies combat.

This is unsupported because the marks on the skeletons could only have been made on already dead animals, which precludes the marks being made during combat.

E
At the time T. rex lived, there were large carnivores on continents other than North America.

This is unsupported because we don’t know anything about the distribution of carnivores across other continents. The stimulus is confined to discussing North America.


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