1.1. Misha and Grisha are writing numbers on the board. Misha writes threes, and Grisha writes fives. In total, they wrote 20 numbers. How many fives were written if the sum of all the numbers is 94?
Answer: 17

Solution. If all 20 numbers were "5", their sum would be 100. We will replace "5" with "3". With each replacement, the sum decreases by 2. Since $100-94=6, 6: 2=3$, we need 3 replacements. Therefore, the number of fives is $20-3=17$.