A bridge is built across a river. One quarter of the bridge is over the left bank of the river and one third of the bridge is over the right bank. The river is $$120\text{m}$$ wide. How long is the bridge? 
Overseas Competition->Knowledge Point->Word Problem Modules->Solving Problems Involving Fractions and Percentages->Finding the Base
The river is $$120\text{m}$$ wide and represents $$\left( 1-\frac{1}{4}-\frac{1}{3} \right)=\frac{5}{12}$$ of the length of the bridge. Therefore $$\frac{1}{12}$$ of the length of the bridge is $$24\text{m}$$. Hence the total length of the bridge is $$12\times 24\text{m}=288\text{m}$$. 