Tính một cách hợp lí: a) 4/15 - (2,9 - 11/15) b) (-36,75) - 37/10 (63,25) - (-6,3)

* Hướng dẫn giải

$$\begin{gathered} a) \frac{4}{15}-\left(2,9-\frac{11}{15}\right)=\frac{4}{15}-2,9+\frac{11}{15} \\ =\frac{4}{15}+\frac{11}{15}-2,9= 1 – 2,9 = – 1,9. \\ b) (-36,75)+\left(\frac{37}{10}-63,25\right)-(-6,3) \\ =(-36,75)+\frac{37}{10}-63,25+6,3 \\ = (– 36,75) – 63,25 + 3,7 + 6,3 \\ = – (36,75 + 63,25) + (3,7 + 6,3) \\ = (– 100) + 10 = – 90. \\ c) 6,5+\left(-\frac{10}{17}\right)-\left(-\frac{7}{2}\right)-\frac{7}{17} \\ =6,5-\frac{10}{17}+3,5-\frac{7}{17}=6,5+3,5-\frac{10}{17}-\frac{7}{17} \\ =(6,5+3,5)-\left(\frac{10}{17}+\frac{7}{17}\right)\text{= 10 – 1 = 9.} \end{gathered}$$

$$\begin{gathered} d) (-39,1).\frac{13}{25}-60,9.\frac{13}{25} \\ =-\frac{13}{25}.(39,1+60,9)=-\frac{13}{25}.100=-52 \end{gathered}$$