Question 19
Barrel $A$ initially contains 11 litres of alcohol and barrel $B$ contains 15 litres of water. Some alcohol is poured from $A$ to $B$, and then some mixture is poured back from $B$ to $A$. The final alcohol concentrations in $A,B$ are $62.5\%$ and $25\%$, respectively. How many litres were poured back from $B$ to $A$?
Use the standard mixture model: the initial alcohol is pure, each mixture is stirred uniformly before transferring, there is no loss, and liquid volumes add.
Use the standard mixture model: the initial alcohol is pure, each mixture is stirred uniformly before transferring, there is no loss, and liquid volumes add.