5. (6 points) Harry Potter is making an enhanced magic potion called "Water of Life and Death" (this is a very strong sedative, made from daffodil root powder and wormwood extract. The concentration of "Water of Life and Death" refers to the percentage of daffodil root powder in the entire potion). He first adds a certain amount of wormwood extract to the regular "Water of Life and Death", making the concentration of "Water of Life and Death" $9 \%$; if he then adds an equal amount of daffodil root powder, the concentration of "Water of Life and Death" becomes $23 \%$; then the concentration of the regular "Water of Life and Death" is $\qquad$ $\%$.
【Solution】Solution: Let the concentration of the ordinary "Life and Death Water" be $x \%$, the initial weight be 100, and the weight of the narcissus root powder and wormwood extract added twice continuously be $a$. Then, $\left\{\begin{array}{l}\frac{\mathrm{x}}{100+\mathrm{a}}=9 \% \\ \frac{\mathrm{x}+\mathrm{a}}{100+2 \mathrm{a}}=23 \%\end{array}\right.$, simplifying to $\left\{\begin{array}{l}100 x-9 a=900 \\ 100 x+54 a=2300\end{array}\right.$, solving gives $x=11$. In conclusion, the concentration of the ordinary "Life and Death Water" is $11 \%$, so the answer is 11.