Question

To mix plaster for a dental model, 45 milliliters (mL) of water are used for 100 grams (g) of plaster. How many milliliters (mL) of water should be used for 250 grams (g) of plaster?

Answer 1

$\begin{array}{ccc}45\ ml&-&100\ g\\\\x\ ml&-&250\ g\end{array}\ \ \ |cross\ multiply\\\\\\100\cdot x=45\cdot250\\\\100x=11,250\ \ \ |divide\ both\ sides\ by\ 100\\\\\huge\boxed{x=1,125\ (ml)}$