Thực hiện phép tính (tính nhanh nếu có thể): a) -2/5 - 1/3 b) 1/2*3/7 + 1/2*44/7

* Hướng dẫn giải

Lời giải

$$\begin{gathered} \mathit{a}\mathbf{)} \frac{-2}{5}-\frac{1}{3} \\ =\frac{-6}{15}-\frac{5}{15} \\ =\frac{-11}{15} \end{gathered}$$ 

$$\begin{gathered} \mathit{b}\mathbf{)} \frac{1}{2}.\frac{3}{7}+\frac{1}{2}.\frac{4}{7} \\ =\frac{1}{2}.\left(\frac{3}{7}+\frac{4}{7}\right) \\ =\frac{1}{2}.1 \\ =\frac{1}{2} \end{gathered}$$

$$\begin{gathered} \mathit{c}\mathbf{)} 1\frac{1}{4}+\mathrm{1,5}-\frac{2}{3} \\ =\frac{5}{4}+\frac{3}{2}-\frac{2}{3} \\ =\frac{15}{12}+\frac{18}{12}-\frac{8}{12} \\ =\frac{25}{12} \end{gathered}$$

$$\begin{gathered} \mathit{d}\mathbf{)}\mathbf{ }(33,2 + 21,5) . 2 \\ = 54,7 . 2 \\ = 109,4. \end{gathered}$$