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

ra 180

= -65.18+65.75-75.65+75.18

=18.(-65+75)

Lời giải:

$=\frac{81}{20}.\frac{4}{9}+\frac{4}{15}: \frac{-4}{7}$

$=\frac{9.9.4}{4.5.9}+\frac{4}{15}.\frac{-7}{4}$

$=\frac{9}{5}+\frac{-7}{15}=\frac{27}{15}+\frac{-7}{15}=\frac{20}{15}=\frac{4}{3}$

\(\dfrac{50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}}{100-\dfrac{12}{13}+\dfrac{6}{19}-\dfrac{6}{23}}\)

\(=\dfrac{50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}}{2\left(50-\dfrac{6}{13}+\dfrac{3}{19}-\dfrac{3}{23}\right)}\)

\(=\dfrac{1}{2}\)

THANK YOU 

CẢM ƠN RẤT NHÌUUUUUUUUUUUUUUUUUUUUUUUUUU

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

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)

\(\dfrac{8}{3}-\left(-\dfrac{4}{3}+3\right)\\ =\dfrac{8}{3}+\dfrac{4}{3}-3\\ =4-3=1\)

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.

$=\frac{6}{7}+\frac{1}{8}-\frac{3}{16}.4=\frac{6}{7}+\frac{1}{8}-\frac{3}{4}$

$=\frac{6}{7}+\frac{1}{8}-\frac{6}{8}=\frac{6}{7}+\frac{-5}{8}$
$=\frac{13}{56}$

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)

\(\dfrac{3}{7}+\left(-\dfrac{1}{5}+\dfrac{-3}{7}\right)\\ =\dfrac{3}{7}-\dfrac{1}{5}-\dfrac{3}{7}=-\dfrac{1}{5}\)

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.

$=(\frac{1}{5}+\frac{4}{5})+(\frac{-2}{9}+\frac{-7}{9})+\frac{16}{17}$

$=\frac{5}{5}+\frac{-9}{9}+\frac{16}{17}$

$=1+(-1)+\frac{16}{17}=\frac{16}{17}$