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13: \(\left(-15\right)+8+7\)
\(=\left(-15\right)+\left(8+7\right)\)
=-15+15
=0
14: \(\left(-8\right)+2+6\)
\(=\left(-8\right)+\left(2+6\right)\)
=-8+8
=0
15: \(\left(-1\right)+3-2\)
\(=\left(-1-2\right)+3\)
=-3+3
=0
16: \(25-8-7\)
\(=25-\left(8+7\right)\)
=25-15
=10
17: \(8-2-6\)
\(=8-\left(2+6\right)\)
=8-8
=0
18: \(\left(-12\right)-3+15\)
\(=\left(-12-3\right)+15\)
=-15+15
=0
![](https://rs.olm.vn/images/avt/0.png?1311)
\(8)\) \(( -6,2 :2 + 3,7 ) : 0,2 = ( -3,1 + 3,7 ) : 0,2 = 0,6 : 0,2 = 3\)
\(9) \) \( 4 \dfrac{11}{23} - \dfrac{9}{14} + 2 \dfrac{12}{23} - \dfrac{5}{14}\)
\(= ( 4 \dfrac{11}{23} + 2 \dfrac{12}{23}) - ( \dfrac{5}{14} + \dfrac{9}{14} )\)
\(= 8- \dfrac{14}{14} \)
\(= 8-1\)
\(=7\)
\(10)\) \(11 \dfrac{1}{4} - ( 2 \dfrac{5}{7} + 5\dfrac{1}{4} )\)
\(= 11 \dfrac{1}{4} - 2 \dfrac{5}{7} - 5\dfrac{1}{4} \)
\(= 11 \dfrac{1}{4} - 5\dfrac{1}{4} - 2 \dfrac{5}{7}\)
\(= 6 - \dfrac{19}{7} = \dfrac{42}{7} - \dfrac{19}{7} = \dfrac{23}{7}\)
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Lời giải:
$=\frac{81}{20}.\frac{4}{9}+\frac{4}{15}: \frac{-4}{7}$
$=\frac{9.9.4}{4.5.9}+\frac{4}{15}.\frac{-7}{4}$
$=\frac{9}{5}+\frac{-7}{15}=\frac{27}{15}+\frac{-7}{15}=\frac{20}{15}=\frac{4}{3}$
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\dfrac{50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}}{100-\dfrac{12}{13}+\dfrac{6}{19}-\dfrac{6}{23}}\)
\(=\dfrac{50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}}{2\left(50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}\right)}\)
\(=\dfrac{1}{2}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
31: (-29)+8-9
\(=\left(-29\right)+\left(8-9\right)\)
\(=-29-1=-30\)
32: \(\left(-14\right)-6-10\)
\(=\left(-14-6\right)-10\)
=-20-10
=-30
33: \(\left(-42\right)+10+2\)
\(=\left(-42\right)+\left(10+2\right)\)
=-42+12
=-30
34: \(\left(-45\right)+25-20\)
\(=\left(-45\right)+\left(25-20\right)\)
=-45+5
=-40
35: \(\left(-60\right)+17+3\)
\(=\left(-60\right)+\left(17+3\right)\)
=-60+20
=-40
36: \(\left(-48\right)+18-10\)
\(=\left(-48+18\right)-10\)
=-30-10
=-40
![](https://rs.olm.vn/images/avt/0.png?1311)
câu d)
\(\dfrac{6}{5}+\left(3+\dfrac{-1}{5}\right)\\ =\dfrac{6}{5}+3+\dfrac{-1}{5}\\ =1+3=4\)
câu e)
\(-\dfrac{3}{5}+\left(-\dfrac{2}{5}+2\right)\\ =\dfrac{-3}{5}+\dfrac{-2}{5}+2\\ =-1+2=1\)
câu f)
\(\dfrac{8}{3}-\left(-\dfrac{4}{3}+3\right)\\ =\dfrac{8}{3}+\dfrac{4}{3}-3\\ =4-3=1\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Lời giải:
g.
$=\frac{-5}{11}+\frac{-6}{11}+1=(\frac{-5}{11}+\frac{-6}{11})+1$
$=\frac{-11}{11}+1=(-1)+1=0$
h.
$=\frac{-17}{13}+\frac{4}{13}+\frac{25}{101}$
$=\frac{-13}{13}+\frac{25}{101}=(-1)+\frac{25}{101}=-(1-\frac{25}{101})$
$=\frac{-76}{101}$
i.
$=\frac{6}{7}+\frac{1}{8}-\frac{3}{16}.4=\frac{6}{7}+\frac{1}{8}-\frac{3}{4}$
$=\frac{6}{7}+\frac{1}{8}-\frac{6}{8}=\frac{6}{7}+\frac{-5}{8}$
$=\frac{13}{56}$
![](https://rs.olm.vn/images/avt/0.png?1311)
CÂU A)
\(\dfrac{5}{3}+\left(7+\dfrac{-5}{3}\right)\\ =\dfrac{5}{3}+7+\dfrac{-5}{3}=7\)
CÂI B)
\(-\dfrac{7}{31}+\left(\dfrac{24}{17}+\dfrac{7}{31}\right)\\ =-\dfrac{7}{31}+\dfrac{24}{17}+\dfrac{7}{31}=\dfrac{24}{17}\)
CÂU C)
\(\dfrac{3}{7}+\left(-\dfrac{1}{5}+\dfrac{-3}{7}\right)\\ =\dfrac{3}{7}-\dfrac{1}{5}-\dfrac{3}{7}=-\dfrac{1}{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
k.
$=\frac{-5}{7}(\frac{2}{11}+\frac{9}{11})+\frac{12}{7}$
$=\frac{-5}{7}.\frac{11}{11}+\frac{12}{7}$
$=\frac{-5}{7}+\frac{12}{7}=\frac{7}{7}=1$
l.
$=(\frac{1}{5}+\frac{4}{5})+(\frac{-2}{9}+\frac{-7}{9})+\frac{16}{17}$
$=\frac{5}{5}+\frac{-9}{9}+\frac{16}{17}$
$=1+(-1)+\frac{16}{17}=\frac{16}{17}$
ra 180
= -65.18+65.75-75.65+75.18
=18.(-65+75)