a: =9/11(7/4+5/4)=9/11x3=27/11

b: \(=\dfrac{28}{5}\cdot\dfrac{5}{8}\cdot\dfrac{5}{4}=\dfrac{28}{8}\cdot\dfrac{5}{4}=\dfrac{140}{32}=\dfrac{35}{8}\)

c: \(=\dfrac{2}{6}+\dfrac{4}{5}\cdot\dfrac{6}{5}-\dfrac{2}{5}=\dfrac{67}{75}\)

a,=(7/4+5/4):11/9

=3:11/9

=27/11

b,=28/5.5/4.5/8

=7.5/8

=35/8

c,=1/3+24/25-2/5

=97/75-2/5

=67/75

7/4:11/9+5/4:11/9

=7/4×9/11+5/4×9/11

=9/11×(7/4+5/4)

=9/11×12/4

=9/11×3

=27/11

b)

28/5:4/5×5/8

=28/5×5/4×5/8

=28/4×5/8

=7×5/8

=35/8

c)

2/3×3/6+4/5:5/6−2/5

=2/6+4/5×6/5−2/5

=1/3+24/25−2/5

=(24/25−2/5)+1/3

=14/25+1/3

=67/75

Bài 1: Tính
a, 1/2 x 2/3 x 3/4 = 1/4
b, 7/8 x 8/9 x 9/10 = 7/10
c, 5/14 x 7/15 x 28/7 = 2/3
d, 2 x 1/2 x 3 x 1/3 x 4 x 1/4 x 5 x 1/5 = 1
Bài 2: Tính
a, 7/20 - ( 5/8 - 3/5 ) = 7/20 - 1/40 = 14/40 - 1/40 = 13/40
b, 5/6 + ( 5/9 - 1/4 ) = 5/6 + 11/36 = 30/36 + 11/36 = 41/36
c, 9/10 - ( 2/5 + 3/10 ) + 7/20 = 9/10 - 7/10 + 7/20 = 2/10 + 7/20 = 4/20 + 7/20 = 11/20.
Bài 3: Tìm x:
a, 1/2 + x = 5/6
x = 5/6 - 1/2
x = 1/3
b, 5/6 - x = 1/3
x = 5/6 - 1/3
x = 1/2
c, x - 1/mấy vậy bạn
d, 1/3 x x = 1/6
x = 1/6 : 1/3
x = 1/2

A\(\frac{1}{2}+\frac{1}{2}=\frac{2}{4}=\frac{1}{2}\)

B\(\frac{3}{8}+\frac{1}{8}=\frac{4}{8}=\frac{1}{2}\)

C\(\frac{7}{9}+\frac{5}{9}=\frac{12}{9}=\frac{4}{3}\)

D\(\frac{1}{6}+\frac{2}{6}=\frac{3}{6}=\frac{1}{2}\)

E\(\frac{3}{8}+\frac{7}{8}=\frac{10}{8}=\frac{5}{4}\)

G\(\frac{2}{5}+\frac{3}{5}=\frac{5}{5}=1\)

*cho mik sửa câu a:

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

Bài 1: Tính rồi rút gọn 

A) \(\frac{1}{2}+\frac{1}{2}=\frac{2}{4}=\frac{1}{2}\)

B)\(\frac{3}{8}+\frac{1}{8}=\frac{4}{8}=\frac{1}{2}\)

C)\(\frac{7}{9}+\frac{5}{9}=\frac{12}{9}=\frac{4}{3}\)

D)\(\frac{1}{6}+\frac{2}{6}=\frac{3}{6}=\frac{1}{2}\)

E)\(\frac{3}{8}+\frac{7}{8}=\frac{10}{8}=\frac{5}{4}\)

G)\(\frac{2}{5}+\frac{3}{5}=\frac{5}{5}=1\)

Mong giúp đc bn. Nếu đúng thì cho mik 1 tích nha ^^

\(a,\frac{2}{7}:\frac{4}{5}=\frac{2}{7}\times\frac{5}{4}=\frac{10}{28}=\frac{5}{14}\)

\(b,\frac{3}{8}:\frac{9}{4}=\frac{3}{8}\times\frac{4}{9}=\frac{12}{72}=\frac{1}{6}\)

\(c,\frac{8}{21}:\frac{4}{7}=\frac{8}{21}\times\frac{7}{4}=\frac{56}{84}=\frac{2}{3}\)

\(d,\frac{5}{8}:\frac{15}{8}=\frac{5}{8}\times\frac{8}{15}=\frac{40}{120}=\frac{1}{3}\)

A,\(\frac{2}{7}:\frac{4}{5}=\frac{2}{7}\times\frac{5}{4}=\frac{10}{28}=\frac{5}{14}\)

B,\(\frac{3}{8}:\frac{9}{4}=\frac{3}{8}\times\frac{4}{9}=\frac{12}{72}=\frac{1}{6}\)

C.\(\frac{8}{21}:\frac{4}{7}=\frac{8}{21}\times\frac{7}{4}=\frac{56}{84}=\frac{2}{3}\)

D.\(\frac{5}{8}:\frac{15}{8}=\frac{5}{8}\times\frac{8}{15}=\frac{40}{120}=\frac{1}{3}\)

Đúng 100%

a, \(\frac{2}{7}:\frac{4}{5}=\)\(\frac{2}{7}x\)\(\frac{5}{4}\)\(\frac{10}{28}=\frac{5}{14}\)

b,\(\frac{3}{8}:\frac{9}{4}\)\(=\frac{3}{8}x\)\(\frac{4}{9}\)\(=\frac{12}{72}=\frac{1}{6}\)

c,\(\frac{8}{21}:\frac{4}{7}\)\(=\frac{8}{21}x\)\(\frac{7}{4}\)\(=\frac{56}{84}=\frac{2}{3}\)

d,\(\frac{5}{8}:\frac{15}{8}\)\(\frac{5}{8}x\)\(\frac{8}{15}=\frac{40}{120}=\frac{1}{3}\)

tk giup mk nha