Answer:
20
Explanation:
According to my research on the repeated measure design, I can say that based on the information provided within the question for this design they would need exactly 20 subjects. This can be said because the repeated measure design is a research method in which the same test subjects are used more than once for different treatments. Which in this case would be three different treatments, and since the scientists concluded they need the same amount of subjects for each treatment then they can use the same 20 subjects for all three treatments.
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