Lời giải:

a. $=-(37+63)+[25+(-25)]+(-9)=-100+0+(-9)=-(100+9)=-109$

b. $=[1+(-3)]+[5+(-7)]+....+[21+(-23)]$

$=\underbrace{(-2)+(-2)+....+(-2)}_{6}=(-2).6=-12$

c. $=-(280+20)+[-(79+21)]=-300+(-100)=-(300+100)=-400$

d. $=[-(27+43)]+[-(208+102)]=-70+(-310)=-(70+310)=-380$

e. $=(38+120)-(12+46)=158-58=100$

f. $=9+15+11+24=(9+11)+(15+24)=20+39=59$

\(21+21+21+...+21+21+16+16+16+...+16.\)           (84 số 21 và 21 số 16)

\(=84\cdot21+21\cdot16=21\left(84+16\right)=21\cdot100=2100\)

21.84+21.16=21(84+16)=21.100=2100

\(A=\frac{9}{15.18}+\frac{9}{18.21}+.....+\frac{9}{89.92}\)

\(A=3.\left(\frac{3}{15.18}+\frac{3}{18.21}+....+\frac{3}{89.92}\right)\)

\(A=3.\left(\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-\frac{1}{21}+......+\frac{1}{89}-\frac{1}{92}\right)\)

\(A=3.\left(\frac{1}{15}-\frac{1}{92}\right)\)

\(A=3.\frac{77}{1380}=\frac{77}{460}\)

$A=\frac{9}{15.18}+\frac{9}{18.21}+.....+\frac{9}{89.92}$

$A=3.\left(\frac{3}{15.18}+\frac{3}{18.21}+....+\frac{3}{89.92}\right)$

$A=3.\left(\frac{1}{15}-\frac{1}{18}+\frac{1}{18}-\frac{1}{21}+......+\frac{1}{89}-\frac{1}{92}\right)$

$A=3.\left(\frac{1}{15}-\frac{1}{92}\right)$

$A=3.\frac{77}{1380}=\frac{77}{460}$

a,\(\frac{1}{5}\times\frac{2}{9}\div\frac{1}{15}\)

\(=\frac{1}{5}\times\frac{2}{9}\times15\)

\(=\left(\frac{1}{5}\times15\right)\times\frac{2}{9}\)

\(=3\times\frac{2}{9}\)

\(=\frac{2}{3}\)

b\(\frac{4}{15}\times\frac{7}{15}\times\frac{5}{4}\)

\(=\left(\frac{4}{15}\times\frac{5}{4}\right)\times\frac{7}{15}\)

\(=\frac{1}{3}\times\frac{7}{15}\)

\(=\frac{7}{45}\)

c,\(\frac{21}{23}\times\frac{5}{11}\times\frac{44}{?}\)

d,\(26\times\frac{13}{42}\div13\)

\(=\left(26\div13\right)\times\frac{13}{42}\)

\(=2\times\frac{13}{42}\)

\(=\frac{13}{21}\)

ờ ờ .......................... hong bt

21/23 x 5/11x 44/35

\(\dfrac{45.21.25}{7.15.36}=\dfrac{3.3.3.5.7.5.5}{7.5.3.3.2.3.2}=\dfrac{25}{4}\)

45\7 x 21\15 x 25/36

=45x21x25/7x15x36

=15x3x7x3x25/7x15x3x12

=3x25/12

=75/12

=25/4

a, \(\frac{4}{20}+\frac{16}{42}+\frac{6}{15}+\frac{-3}{5}+\frac{-10}{21}+\frac{3}{20}\)

\(=\left(\frac{4}{20}+\frac{-3}{5}+\frac{6}{15}+\frac{3}{20}\right)\)\(+\left(\frac{16}{42}+\frac{2}{21}+\frac{-10}{21}\right)\)

\(=\left(\frac{4}{20}+\frac{-12}{20}+\frac{8}{20}+\frac{3}{20}\right)\)\(+\left(\frac{8}{21}+\frac{2}{21}+\frac{-10}{21}\right)\)

\(=\frac{3}{20}\)

b,\(\frac{42}{46}+\frac{250}{186}+\frac{-2121}{2323}+\frac{-125125}{143143}\)

\(=\frac{21}{23}+\frac{125}{93}+\frac{-21}{23}+\frac{-125}{143}\)

\(=\left(\frac{21}{23}+\frac{-21}{23}\right)+\left(\frac{125}{93}+\frac{-125}{143}\right)\)

\(=\frac{6250}{13299}\)

\(\Rightarrow A=\left(\frac{27}{23}-\frac{4}{23}\right)+\left(\frac{5}{21}+\frac{16}{21}\right)+\frac{1}{2}\)

\(\Rightarrow A=1+1+\frac{1}{2}\)

\(\Rightarrow A=\frac{5}{2}\)

tíc mình nha

A=1+1+1/2

A=5/2

=5/2 nhé

a)15/34-8/21+19/34-34/21

 =(15/34+19/34)+(-8/21-34/21)

= 34/34+(-42/21)

=1+(-2)

=-1

đề tự ghi lại nha 

=\(\left(\frac{15}{34}+\frac{19}{34}\right)+\left(\frac{-8}{21}-\frac{34}{21}\right)\)

=\(\frac{34}{34}+\frac{-42}{21}\)

=\(1+\left(-2\right)\)

=\(-1\)