5. There is a five-digit positive odd number $x$. Replace all 2s in $x$ with 5s, and all 5s with 2s, keeping other digits unchanged, to get a new five-digit number, denoted as $y$. If $x$ and $y$ satisfy the equation $y=2(x+1)$, then $x$ is $\qquad$.
5. 29995

Solution First, the ten-thousands digit of $x$ is clearly 2, so the ten-thousands digit of $y$ must be 5; next, the thousands digit of $x$ must be greater than 5, but the hundreds digit multiplied by 2 can carry at most 1 to the thousands place, so the thousands digit can only be 9. By similar reasoning, the first four digits of $x$ are $2,9,9,9. The units digit of $x$ can only be $1,3,5,7,9$. Upon inspection, the units digit of $x$ can only be 5, so $x$ is 29995.