Giải bài 4 trang 27

Đề bài

Tính giá trị các biểu thức sau:

a)$A=\left[\left(-0,5\right)-\frac{3}{5}\right]:\left(-3\right)+\frac{1}{3}-\left(-\frac{1}{6}\right):\left(-2\right)$

b)$B=\left(\frac{2}{25}-0,036\right):\frac{11}{50}-\left[\left(3\frac{1}{4}-2\frac{4}{9}\right)\right].\frac{9}{29}$

Lời giải chi tiết

a)

$\begin{array}{c}A=\left[\left(-0,5\right)-\frac{3}{5}\right]:\left(-3\right)+\frac{1}{3}-\left(-\frac{1}{6}\right):\left(-2\right)\\ =\left(\frac{-5}{10}-\frac{6}{10}\right).\frac{-1}{3}+\frac{1}{3}-\frac{-1}{6}.\frac{-1}{2}\\ =\frac{-11}{10}.\frac{-1}{3}+\frac{1}{3}-\frac{1}{12}\\ =\frac{11}{30}+\frac{1}{3}+\frac{-1}{12}\\ =\frac{22}{60}+\frac{20}{60}-\frac{5}{60}\\ =\frac{37}{60}\end{array}$

b)

$\begin{array}{c}B=\left(\frac{2}{25}-0,036\right):\frac{11}{50}-\left[\left(3\frac{1}{4}-2\frac{4}{9}\right)\right].\frac{9}{29}\\ =\left(\frac{2}{25}-\frac{36}{1000}\right).\frac{50}{11}-\left[\left(\frac{13}{4}-\frac{22}{9}\right)\right].\frac{9}{29}\\ =\left(\frac{20}{250}-\frac{9}{250}\right).\frac{50}{11}-\left[\left(\frac{117}{36}-\frac{88}{36}\right)\right].\frac{9}{29}\\ =\frac{11}{250}.\frac{50}{11}-\frac{29}{36}.\frac{9}{29}\\ =\frac{1}{5}-\frac{1}{4}\\ =\frac{4}{20}-\frac{5}{20}\\ =\frac{-1}{20}\end{array}$