$$2 \frac{2}{9}+4 \frac{1}{18}-1 \frac{1}{2}=?$$ Let the missing number be $x$ $$x=\frac{20}{9}+\frac{73}{18}-\frac{3}{2}$$ LCM of 9, 18 and 2 is 18. $$\begin{aligned} & =\frac{40+73-27}{18}=\frac{86}{18} \\ & =\frac{43}{9}=4 \frac{7}{9} \end{aligned}$$
Explanation as extracted from the printed page; notation may be imperfect.