1. Write $20 \uparrow 1.1$ and $20 \uparrow 1.11$ on a piece of paper, cross out some numbers so that the sum of the remaining numbers is 19.93, please explain how to do it.
1. If the paper is left with $n$ 1.11s, then the last digit of $n$ should be 3, because $n \leqslant 20$. So $n=3$ or $n=13$. From this, it can be deduced that 7 1.11s and 15 1.1s should be crossed out.