7.1. Write the number 1.11 ten times and the number 1.01 eleven times. Cross out one or several numbers so that the sum of the remaining numbers is equal to 20.19.
Answer: 1,$11 ; 1,11 ; 1,11 ; 1,11 ; 1,11 ; 1,11 ; 1,11 ; 1,11 ; 1,11 ; 1,11 ; 1,01 ; 1,01 ; 1,01 ; 1,01 ;$ 1,$01 ; 1,01 ; 1,01 ; 1,01 ; 1,01$. (Struck out numbers 1,01 and 1,01.)

Solution. The sum of all the written numbers is 10$\cdot$1,11 + 11$\cdot$1,01 = 22,21. This is 2,02 more than the required sum. That is, it is enough to strike out two numbers $1,01$.

One can also verify directly that the sum of the numbers remaining after the strikeout is 20,19.

Grading criteria.

«+» The correct answer is provided and it is shown that it satisfies the condition

«土» The correct answer is provided, but it is not shown why it satisfies the condition

«-» An incorrect answer is provided or the problem is not solved