Fix train split

A total of 12 edits; task numbering matches the sequential index (starting from 0) of the task in the original dataset.

1. #269, #270 deleted, simple problems with multiple-answer choice
2. #14 unclear problem statement, switched to the original one https://problems.ru/view_problem_details_new.php?id=111330
3. #238 deleted, simple problem same as #237 but with incorrect answer
4. #262 changed $\(\sqrt{a} + \sqrt{b}\)$ --> $\(\sqrt{a + \sqrt{b}}\)$, check original problem statement https://clck.ru/3VSFZn
5. #152 corrected \times --> \\times
6. #40 maximal length is 24\sqrt{5}, problem statement is corrected for answer to be equal 24
7. #224-#229 in all of this problems problem statement is switched from "Сколькими способами можно это сделать?" to "Сколько различных чисел кратных 5 можно получить таким образом?". In #229 answer was fixed
8. #41 deleted, requires picture https://problems.ru/view_problem_details_new.php?id=64578
9. #160 deleted, very simple problem, but the answer is not unique if negative numbers are allowed
10. #251 deleted, requires picture
11. #76 x equals to (\sqrt{5} - 1)/2 \approx 0.618, answer is corrected
12. #268 corrected \times --> \\times

data/train-00000-of-00001.parquet

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