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21 possibly, he blocked the window from the outside, but it remained square from the inside.
22 2 3 6 years
25 those who wanted to get married often opened it to check if it was boiling or not; the temperature of the air in the teapot drops at this time. But the other one didn't care, and she didn't open the teapot.
26 Take one coin from the first hat, two from the second, and so on. Then, the difference in grams will be the weight of the hat.
29 one divides the piles, the other chooses which one.