Adding five of the six fractions $$\frac{1}{2}$$, $$\frac{2}{3}$$, $$\frac{1}{4}$$, $$\frac{1}{6}$$, $$\frac{1}{9}$$ and $$\frac{1}{18}$$ gives a total of $$1.5$$.  Which of the fractions is not used? 
Overseas Competition->Knowledge Point->Calculation Modules->Fractions->Operations of Fractions
The sum of the five given fractions is $$\frac{1}{2}+\frac{2}{3}+\frac{1}{4}+\frac{1}{6}+\frac{1}{9}+\frac{1}{18}=\frac{18+24+9+6+4+2}{36}$$.  $$\frac{63}{36}= \frac{7}{4}=1 \frac{3}{4}$$.  So the fraction which is not used is $$1 \frac{3}{4}-1 \frac{1}{2}=\frac{1}{4}$$. 