## Task B-1.2.

If the digit $1 \mathrm{~s}$ is appended to both the left and right sides of a two-digit number, the resulting number is 21 times greater than the original number. Determine that two-digit number.
## Solution.

Let $\overline{x y}$ be the desired number, and $\overline{1 x y 1}$ be the new number.

Then $\overline{1 x y 1}=21 \cdot \overline{x y}$.

$1000+100 x+10 y+1=21 \cdot(10 x+y)$

(1 point)

$10 x+y=91$

$\overline{x y}=91$