Pail $$A$$ contains $$\frac{2}{3}$$ as much water as Pail $$B$$. When $$4$$ litres of water is poured from Pail $$B$$ into Pail $$A$$. Pail $$A$$ will contain $$\frac{7}{8}$$ as much water as Pail $$B$$. What is the total amount of water (in litres) in both pails? 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Finding the Base