2.4. At the beginning of January 2018, the mother and father started saving for a new apartment. Their salaries were received on the 15th of each month, and after each salary, the mother saved 12 thousand rubles, and the father saved 22 thousand rubles. One day, the father's income decreased, and the family decided to spend all of his salary, and only save from the mother's salary. On October 11, 2020, it turned out that the mother's savings were twice as much as the father's savings. From which month and year did the father's salary go towards the family's current expenses? Specify the month and year
Answer: October, 2018

Solution. By October 2020, the years 2018 and 2019 had fully passed, and 9 months of 2020 had also passed, totaling 33 months. The mother's savings from her salary amounted to $33 \cdot 12 = 396$ thousand rubles. Therefore, the father's savings amounted to (396:2):22 = 9 months. This means the income reduction occurred after 9 months, that is, in October 2018.