\(1.\\ a,\dfrac{36}{72}=\dfrac{36:36}{72:36}=\dfrac{1}{2}\\ b,\dfrac{15}{125}=\dfrac{15:5}{125:5}=\dfrac{3}{25}\\2.\\ a,\dfrac{4}{9}=\dfrac{4\times4}{9\times4}=\dfrac{16}{36}\\ \dfrac{5}{4}=\dfrac{5\times9}{4\times9}=\dfrac{45}{36}\\ b,\dfrac{25}{100}giữnguyên\\ \dfrac{20}{50}=\dfrac{20\times2}{50\times2}=\dfrac{40}{100}\\ c,\dfrac{5}{9}=\dfrac{5\times5}{9\times5}=\dfrac{25}{45}\\ \dfrac{4}{5}=\dfrac{4\times9}{5\times9}=\dfrac{36}{45}\\ \dfrac{5}{3}=\dfrac{5\times15}{3\times15}=\dfrac{75}{45}\)

\(a,14,75-7,15:5+2,6\times3,5\\ =14,75-1,43+9,1\\ =13,32+9,1\\ =22,42\\ b,13,5:4,5\times2,4+\left(156,9-80,6\right)\\ =13,5:4,5\times2,4+76,3\\ =3\times2,4+76,3\\ =7,2+76,3\\ =83,5\\ c,1,25\times4,2+119,6:5,2-23,19\\ =5,25+23-23,19\\ =28,25-23,19\\ =5,06\)

\(452-\left(67-75+452\right)\\ =452-67+75-452\\ =\left(452-452\right)-67+75\\ =-67+75\\ =8\)