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1:48
The Will Rogers Phenomenon
both averages go up, nobody changes
Group A holds the numbers 1, 2, 3 and 4, with an average of 2.5. Group B holds 5, 6, 7, 8 and 9, with an average of 7. Move the 5 from group B to group A.
Source: A classic puzzle, retold by INFINITE SUM and fact-checked against our curated notes
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