3. On a $6 \times 6$ checkerboard, there are chips. It turns out that for each number $n$ from 2 to 10, there is a chip such that in the same column and the same row with it, there are exactly $n$ chips in total (not counting the chip itself). What is the maximum number of chips that can be on the board?
Answer: 21

## Examples of answer recording:

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## 9th grade.

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