To determine which two quantitative variables might produce a straight line in a scatterplot, we need to consider the nature of their relationship. A straight line indicates a linear relationship between the two variables.
Among the provided options:
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Time spent playing video games and adult shoe size - This relationship is unlikely to be linear, as there is no logical reasoning to suggest that time spent gaming would correlate directly with shoe size.
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Time spent studying for an exam and the grade on the exam - This has the potential to be a linear relationship, as generally, more time spent studying can lead to higher grades, assuming the study methods are effective.
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Time spent mowing the lawn and the number of snakes in the yard - There is no expected correlation here, as the number of snakes in the yard isn't likely to depend linearly on the time spent mowing the lawn.
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Time it takes to get to the grocery store and the number of grocery items purchased - This relationship is also not guaranteed to be linear. The number of items purchased could vary widely regardless of the time it took to get to the store.
Based on this analysis, the pair that is most likely to show a linear relationship is:
Time spent studying for an exam and the grade on the exam.