Bài 1 (2 điểm): Thực hiện phép tính a) $\frac{-5}{11}$ + $\frac{1}{2}$ +$\frac{7}{8}$ +$\frac{-6}{11}$ + $\frac{2}{16}$  b) $\frac{5}{4}$ .$\frac{1}{7}$ +$\frac{3}{4}$ .$\frac{5}{7}$ - $1\frac{5}{7}$ c) $\frac{1}{4}$ - ($\frac{1}{4}$+ $4\frac{1}{2}$ ) + $(-3)^{2}$ : $\frac{27}{2}$ 

Đáp án:

a.$\dfrac12$

b.$-1$

c.$\dfrac{-23}6$

Giải thích các bước giải:

a.Ta có:

$\dfrac{-5}{11}+\dfrac{1}2+\dfrac78+\dfrac{-6}{11}+\dfrac2{16}$

$=(\dfrac{-5}{11}+\dfrac{-6}{11})+\dfrac{1}2+\dfrac78+\dfrac2{16}$

$=\dfrac{-5-6}{11}+\dfrac{8}{16}+\dfrac{14}{16}+\dfrac2{16}$

$=\dfrac{-11}{11}+\dfrac{8+14+2}{16}$

$=-1+\dfrac{24}{16}$

$=\dfrac{24}{16}-1$

$=\dfrac{24-16}{16}$

$=\dfrac{8}{16}$

$=\dfrac12$

b.Ta có:

$\dfrac{5}4\cdot\dfrac17+\dfrac34\cdot\dfrac57-1\dfrac57$

$=\dfrac{1}4\cdot\dfrac57+\dfrac34\cdot\dfrac57-\dfrac{12}7$

$=\dfrac57\cdot (\dfrac14+\dfrac34)-\dfrac{12}7$

$=\dfrac57\cdot 1-\dfrac{12}7$

$=\dfrac57-\dfrac{12}7$

$=\dfrac{5-12}7$

$=\dfrac{-7}7$
$=-1$

c.Ta có:

$\dfrac14-(\dfrac14+4\dfrac12)+(-3)^2:\dfrac{27}2$

$=\dfrac14-(\dfrac14+\dfrac92)+9:\dfrac{27}2$

$=\dfrac14-\dfrac14-\dfrac92+9\cdot\dfrac2{27}$

$=0-\dfrac92+\dfrac23$

$=\dfrac{-9}2+\dfrac23$

$=\dfrac{-27}6+\dfrac{4}6$

$=\dfrac{-27+4}6$

$=\dfrac{-23}6$