a) \(\dfrac{2}{5}\cdot\dfrac{1}{7}+\dfrac{2}{5}\cdot\dfrac{5}{7}+\dfrac{2}{5}\)

\(=\dfrac{2}{5}\left(\dfrac{1}{7}+\dfrac{5}{7}+1\right)\)

\(=\dfrac{2}{5}\cdot\dfrac{13}{7}=\dfrac{26}{35}\)

b) \(\dfrac{1}{5}+\dfrac{2}{8}+\dfrac{4}{5}+\dfrac{7}{8}-\dfrac{1}{8}\)

\(=\left(\dfrac{1}{5}+\dfrac{4}{5}\right)+\left(\dfrac{2}{8}+\dfrac{7}{8}-\dfrac{1}{8}\right)\)

\(=1+1=2\)

c)\(\dfrac{24}{36}\cdot\dfrac{10}{12}\cdot36\)

\(=\dfrac{24\cdot10\cdot36}{36\cdot12}=\dfrac{12\cdot2\cdot10\cdot36}{12\cdot36}\)

\(=2\cdot10=20\)

  1/2x1/3+1/3x1/4+1/4x1/5+1/5x1/6+1/6x1/7+1/7x1/8+1/8x1/9

=7/18

19/20x2/100+19/20x2/100

= [19/20+19/20]x2/100

= 38/20x2/100

= 19/500

75/76x102/100-75/76x2/100

= [102/100-2/100]x75/76

= 1x75/76

= 75/76

3x7/10+7/10x5+2x7/10

= [3+5+2]x7/10

= 10x7/10

= 7

giá trị biểu thức 

2/5+2/3x3/4

= 2/5+1/6

= 17/30

1/2x1/3-1/8

= 1/6-1/8

= 1/24

[1/2+1/3]:3/9

= 5/6:3/9

= 5/2

                       nhớ tick cho tớ nhé

rùi đó

giúp mk nha , chiều mk đi hok rồi 

a, 12/5.4-4.7/5=4.(12/5-7/5)=4.1=4

b, 14/3-1/5/9.21/4=14/3-14/9.21/4=14/3-49/6=-7/2

c, 2/6.3/7:21/4=1/7:21/4=4/147

d, 2/3/5:2/1/4+5/2=13/5:9/4+5/2=52/45+5/2=329/90

e, 3/2/5.1/4/7+12/35=17/5.11/7+12/35=187/35+12/35=199/35

\(\dfrac{4}{5}-\dfrac{2}{5}\times\dfrac{1}{4}=\dfrac{4}{5}-\dfrac{1}{10}=\dfrac{8}{10}-\dfrac{1}{10}=\dfrac{7}{10}\)

\(\dfrac{1}{4}+\dfrac{3}{4}:\dfrac{1}{8}=\dfrac{1}{4}+\dfrac{3}{4}\times8=\dfrac{1}{4}+6=\dfrac{1}{4}+\dfrac{24}{4}=\dfrac{25}{4}\)

\(\)\(\dfrac{11}{10}-\dfrac{2}{5}:\dfrac{1}{3}=\dfrac{11}{10}-\dfrac{2}{5}\times3=\dfrac{11}{10}-\dfrac{6}{5}=\dfrac{11}{10}-\dfrac{12}{10}=-\dfrac{1}{10}\)

4/5-2/5.1/4

=4/5-1/10

=8/10-1/10

=7/10

1/4+3/4:1/8

=1/4+3/4.8

=1/4+6

=1/4+24/4

=25/4

11/10-2/5:1/3

=11/10-2/5.3

=11/10-6/5

=11/10-12/10

=-1/10

\(\dfrac{4}{5}-\dfrac{2}{5}x\dfrac{1}{4}=\dfrac{4}{5}-\dfrac{2}{20}=\dfrac{16}{20}-\dfrac{2}{20}=\dfrac{14}{20}=\dfrac{7}{10}\)

\(\dfrac{1}{4}+\dfrac{3}{4}:\dfrac{1}{8}=\dfrac{1}{4}+\dfrac{3}{4}x\dfrac{8}{1}=\dfrac{25}{4}\)

\(\dfrac{11}{10}-\dfrac{2}{5}:\dfrac{1}{3}=\dfrac{11}{10}-\dfrac{2}{5}x\dfrac{3}{1}=\dfrac{11}{10}-\dfrac{6}{5}=\dfrac{11}{10}-\dfrac{12}{10}=-\dfrac{1}{10}\)

\(\frac{2}{3}+\frac{5}{9}-\frac{3}{4}=\frac{24}{36}+\frac{20}{36}-\frac{15}{36}\)\(=\frac{29}{36}\)

\(\frac{2}{5}\times\frac{1}{4}:\frac{3}{8}=\frac{2\times1\times8}{5\times4\times3}=\frac{16}{60}=\frac{4}{15}\)

a) 2/3 + 5/9 = 11/9 - 3/4 = 17/36

b) 2/5 * 1/4 = 1/10 : 3/8 = 4/15

Mik cũng ko chắc nữa có sai thì cho mink sorry bạn nha

a) 2/3+5/9-3/4

=11/9-3/4

=17/36

b) 2/5x1/4:3/8

=1/10:3/8

=4/15

chúc bạn học tốt nha!!!!!

tham khảo

a. 5/8

b. 29/28

c. -1/36

d. -41/24

e. -341/273

f. -17/5

g. -4