Bài 4:
\(B=\left[\left(-\dfrac{1}{2}\right):0,07-\dfrac{1}{5}:0,07\right]\left(\dfrac{3}{2}\cdot2,5+1,5\cdot\dfrac{15}{2}\right)\)
\(=\left[\left(-\dfrac{1}{2}\right)\cdot\dfrac{100}{7}-\dfrac{1}{5}\cdot\dfrac{100}{7}\right]\left(\dfrac{3}{2}\cdot\dfrac{5}{2}+\dfrac{3}{2}\cdot\dfrac{15}{2}\right)\)
\(=\dfrac{100}{7}\cdot\left(-\dfrac{1}{2}-\dfrac{1}{5}\right)\cdot\dfrac{3}{2}\left(\dfrac{5}{2}+\dfrac{15}{2}\right)\)
\(=\dfrac{100}{7}\cdot-\dfrac{7}{10}\cdot\dfrac{3}{2}\cdot\dfrac{20}{2}\)
\(=-10\cdot15\)
\(=-150\)
Chọn C
Bài 5:
\(A=\left(\dfrac{20}{21}-1\right):\left(\dfrac{4141}{4242}-1\right):\left(\dfrac{636363}{646464}-1\right)\)
\(=\left(1-\dfrac{1}{21}-1\right):\left(\dfrac{41\cdot101}{42\cdot101}-1\right):\left(\dfrac{63\cdot10101}{64\cdot10101}-1\right)\)
\(=\left(-\dfrac{1}{21}\right):\left(\dfrac{41}{42}-1\right):\left(\dfrac{63}{64}-1\right)\)
\(=\left(-\dfrac{1}{21}\right):\left(1-\dfrac{1}{42}-1\right):\left(1-\dfrac{1}{64}-1\right)\)
\(=\left(-\dfrac{1}{21}\right):\left(-\dfrac{1}{42}\right):\left(-\dfrac{1}{64}\right)\)
\(=\left(-\dfrac{1}{21}\right)\cdot\left(-42\right)\cdot\left(-64\right)\)
\(=\left(-\dfrac{1}{21}\cdot-42\right)\cdot64\)
\(=2\cdot64\)
\(=128\)
Chọn A
help bài 3 câu a ,b, và c help
