1. In a certain month, three Sundays fell on even dates. What day of the week was the 20th of this month?
Solution. Sundays in one month alternate between falling on even and odd dates. Since 3 of them fell on even dates, there were a total of 5 Sundays in this month, so the first one could only have been on the 2nd, from which it follows that the 20th was a Thursday.

Answer: Thursday.

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