[tex]1l=1dm^3\\1dm=10cm\to1dm^3=(10cm)^3=1000cm^3\\\\1l=1000cm^3\\-------------\\ \begin{array}{ccc}400cm^3&-&25\%\\1000cm^3+x&-&100\%\end{array}\\cross\ multiply\\25(1000+x)=400\times100\\25000+25x=40000\ \ \ \ \ |subtract\ 25000\ from\ both\ sides\\25x=15000\ \ \ \ |divide\ both\ sides\ by\ 25\\\boxed{x=600\ (cm^3)}\\\\Answer:Must\ be\ added\ 600cm^3\ of\ water.[/tex]
