In the decimal representation of a number, there is a zero. By crossing out this zero, the number decreased by 9 times. In which position was this zero? 

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Let $\overline{A 0 B}$ be the decimal representation of the desired number, where $A$ is a $k$-digit number, and $B$ is an $m$-digit number. Then $\overline{A B 0}=10 \cdot \overline{A B}=$ $\overline{A 0 B}+\overline{A B}$, from which $\overline{B 0}=B+\overline{A B}$. This means that the number $\overline{A B}$ consists of no more than $m+1$ digits, that is, $A-$ is a digit.

## Answer

In the second position from the left.

## Problem