Tính giá trị cho các biểu thức sau: a -3/8 + 5/12

* Hướng dẫn giải

a) $\frac{-3}{8}+\frac{5}{12}$

= $\frac{-9}{24}+\frac{10}{24}$

= $\frac{-9+10}{24}$

= $\frac{1}{24}$

b) $\frac{-5}{7}.\frac{2}{11}+\frac{-5}{7}.\frac{9}{11}+\frac{5}{7}$

= $\frac{-5}{7}.\frac{2}{11}+\frac{-5}{7}.\frac{9}{11}+\frac{-5}{7}.(-1)$

= $\frac{-5}{7}.[\frac{2}{11}+\frac{9}{11}+(-1)]$

= $\frac{-5}{7}.[\frac{2+9}{11}+(-1)]$

= $\frac{-5}{7}.[1+(-1)]$

= $\frac{-5}{7}.0$ = 0.

c) $\frac{2}{-11}.6\frac{2}{7}+\frac{4}{7}:4-2$

= $\frac{-2}{11}.\frac{44}{7}+\frac{4}{7}.\frac{1}{4}-2$

= $\frac{-8}{7}+\frac{1}{7}-2$

= $\frac{-7}{7}-2$ = -1 - 2 = -3

d) 1,75 : 5 + 2,5 . (4² – 4 . 4,1)

= 1,75 : 5 + 2,5 . (16 – 4 . 4,1)

= 1,75 : 5 + 2,5 . (16 – 16,4)

= 1,75 : 5 + 2,5 . (−0,4)

= 0,35 − 1

= −0,65.