\(2\dfrac{1}{5}+3\dfrac{4}{9}=\dfrac{2\times5+1}{5}+\dfrac{3\times9+4}{9}=\dfrac{11}{5}+\dfrac{31}{9}=\dfrac{11\times9+31\times5}{45}=\dfrac{254}{45}\\ 5\dfrac{3}{7}-3\dfrac{5}{6}=\dfrac{5\times7+3}{7}-\dfrac{3\times6+5}{6}=\dfrac{38}{7}-\dfrac{23}{6}=\dfrac{38\times6-23\times7}{42}=\dfrac{67}{42}\)
\(2\dfrac{1}{5}+3\dfrac{4}{9}=\dfrac{11}{5}+\dfrac{31}{9}=\dfrac{99}{45}+\dfrac{279}{45}=\dfrac{99+279}{45}=\dfrac{42}{5}\)
\(5\dfrac{3}{7}-3\dfrac{5}{6}=\dfrac{38}{7}-\dfrac{23}{6}=\dfrac{228}{42}-\dfrac{161}{42}=\dfrac{228-161}{42}=\dfrac{67}{42}\)
\(2\dfrac{1}{5}+3\dfrac{4}{9}=\dfrac{11}{5}+\dfrac{31}{9}=\dfrac{99}{45}+\dfrac{155}{45}=\dfrac{254}{45}\)
\(5\dfrac{3}{7}-3\dfrac{5}{6}=\dfrac{38}{7}-\dfrac{23}{6}=\dfrac{228}{42}-\dfrac{161}{42}=\dfrac{67}{42}\)
A)2 và 1/5 + 3 và 4/9 đổi thành=> 11/5 + 31/9 = 99/45 + 135/45 = 234/45
B)5 và 3/7-3 và 5/6₫ổi thành=>
38/7-23/6=228/42-161/42=67/42
