\(\begin{array}{l}a)\,\frac{{20 - a}}{{24 - a}} = \frac{2}{3}\,\,\,\,\,\,\,dk:\,\,\,a \ne 24\\ \Rightarrow 2 \times \left( {24 - a} \right) = 3 \times \left( {20 - a} \right)\\ \Rightarrow 48 - 2 \times a = 60 - 3 \times a\\ \Rightarrow 3 \times a - 2 \times a = 60 - 48\\ \Rightarrow a = 12\\b)\,\frac{{20 - a}}{{22 - a}} = \frac{3}{7}\\ \Rightarrow 7 \times \left( {20 - a} \right) = 3 \times \left( {22 - a} \right)\\ \Rightarrow 140 - 7 \times a = 66 - 3 \times a\\ \Rightarrow 7 \times a - 3 \times a = 140 - 66\\ \Rightarrow 4 \times a = 74\\ \Rightarrow a = 74:4 = 18,5\\c)\,\frac{{30 - a}}{{36 - a}} = \frac{1}{2}\\d)\,\frac{{48 - a}}{{52 - a}} = \frac{4}{5}\end{array}\)

c và d em làm tương tự nhé