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Câu 1: A
Câu 2: C
Câu 3: 1/4 quả dưa nặng 0,5kg
Câu 4: =-3-1,3+5,6=4,3-3=1,3
\(a.\)
\(-\dfrac{5}{9}\cdot\dfrac{12}{35}=\dfrac{\left(-5\right)\cdot12}{9\cdot35}=\dfrac{-60}{315}=-\dfrac{4}{21}\)
\(b.\)
\(\left(-\dfrac{5}{8}\right)\cdot-\dfrac{6}{55}=\dfrac{\left(-5\right)\cdot\left(-6\right)}{8\cdot55}=\dfrac{30}{440}=\dfrac{3}{44}\)
\(c.\)
\(\left(-7\right)\cdot\dfrac{2}{5}=-\dfrac{14}{5}\)
\(d.\)
\(-\dfrac{3}{8}\cdot\left(-6\right)=\dfrac{-3\cdot\left(-6\right)}{8}=\dfrac{18}{8}=\dfrac{9}{4}\)
\(\left(x+\dfrac{2}{3}\right)+\dfrac{1}{11}=\left(\dfrac{10}{-33}.\dfrac{11}{8}\right).\dfrac{24}{-55}\)
\(\Rightarrow\left(x+\dfrac{2}{3}\right)+\dfrac{1}{11}=\dfrac{-5}{12}.\dfrac{24}{-55}\)
\(\Rightarrow\left(x+\dfrac{2}{3}\right)+\dfrac{1}{11}=\dfrac{2}{11}\)
\(\Rightarrow x+\dfrac{2}{3}=\dfrac{2}{11}-\dfrac{1}{11}\)
\(\Rightarrow x+\dfrac{2}{3}=\dfrac{1}{11}\)
\(\Rightarrow x=\dfrac{1}{11}-\dfrac{2}{3}\)
\(\Rightarrow x=-\dfrac{19}{33}\)
\(\dfrac{1}{5}+\dfrac{2}{11}< \dfrac{x}{55}< \dfrac{2}{5}+\dfrac{1}{5}\)
\(\dfrac{11+10}{55}< \dfrac{x}{55}< \dfrac{3}{5}\)
\(\dfrac{21}{55}< \dfrac{x}{55}< \dfrac{33}{55}\)
Vậy \(x\in\left\{22;23;24;...\right\}\)
\(\dfrac{1}{5} = \dfrac{{1.3}}{{5.3}} = \dfrac{3}{{15}}\);
\(\dfrac{{ - 10}}{{55}} = \dfrac{{ - 10:5}}{{55:5}} = \dfrac{{ - 2}}{{11}}\)
Vậy các cặp phân số bằng nhau là: \(\dfrac{1}{5} = \dfrac{3}{{15}}; \dfrac{{ - 10}}{{55}} = \dfrac{{ - 2}}{{11}}\)
\(\dfrac{1}{55^2}.5^4.\left(-11\right)^2.55^5.\left(\dfrac{1}{5^2}\right)^2:\left(5^3.11^6\right)\)
\(=\dfrac{5^4.11^2.5^5.11^5}{5^2.11^2}.\dfrac{1}{5^4.5^3.11^6}\)
\(=\dfrac{5^9.11^7}{5^9.11^8}=\dfrac{1}{11}\)
\(=\dfrac{1}{5^2\cdot11^2}\cdot5^4\cdot11^2\cdot55^5\cdot\left(\dfrac{1}{5}\right)^2\cdot\dfrac{1}{5^3\cdot11^6}\)
\(=5^2\cdot5^5\cdot11^5\cdot\dfrac{1}{5^2\cdot5^3\cdot11^6}\)
\(=\dfrac{11^5}{11^6}\cdot\dfrac{5^7}{5^5}=\dfrac{25}{11}\)
Chọn C