a) \(\left(\frac{1}{5}+\frac{3}{5}\right)\times\frac{1}{4}\)

\(=\frac{4}{5}\times\frac{1}{4}\)

\(=\frac{4}{20}=\frac{1}{5}\)

\(\left(\frac{1}{5}+\frac{3}{5}\right)\times\frac{1}{4}=\frac{1}{5}\times\frac{1}{4}+\frac{3}{5}\times\frac{1}{4}\)

                                  \(=\frac{1}{20}+\frac{3}{20}\)

                                    \(=\frac{4}{20}=\frac{1}{5}\)

b) \(\left(\frac{7}{9}-\frac{2}{9}\right)\times\frac{3}{2}\)

\(=\frac{5}{9}\times\frac{3}{2}\)

\(=\frac{15}{18}=\frac{5}{6}\)

\(\left(\frac{7}{9}-\frac{2}{9}\right)\times\frac{3}{2}=\frac{7}{9}\times\frac{3}{2}-\frac{2}{9}\times\frac{3}{2}\)

                                  \(=\frac{21}{18}-\frac{6}{18}\)

                                   \(=\frac{15}{18}=\frac{5}{6}\)

c) \(\left(\frac{11}{13}-\frac{9}{13}\right)\times\frac{39}{21}\)

\(=\frac{2}{13}\times\frac{39}{21}\)

\(=\frac{78}{273}=\frac{2}{7}\)

\(\left(\frac{11}{13}-\frac{9}{13}\right)\times\frac{39}{21}=\frac{11}{13}\times\frac{39}{21}-\frac{9}{13}\times\frac{39}{21}\)

                                       \(=\frac{429}{273}-\frac{351}{273}\)

                                         \(=\frac{78}{273}=\frac{2}{7}\)

a,\(\left(\frac{1}{5}+\frac{3}{5}\right)x\frac{1}{4}\)

=\(\frac{4}{5}x\frac{1}{4}\)

=\(\frac{4}{20}\)

=\(\frac{1}{5}\)

,\(\left(\frac{1}{5}+\frac{3}{5}\right)x\frac{1}{4}\)

=\(\frac{4}{5}x\frac{1}{4}\)

=\(\frac{4x1}{5x4}\)

=\(\frac{1x1}{5x1}\)

=\(\frac{1}{5}\)

9 phân số bạn nhé

có 10 phân số 

TA THẤY : \(\frac{13}{30}=\frac{39}{90},\frac{14}{30}=\frac{42}{90}\)

GIỮA \(\frac{39}{90},\frac{42}{90}\)CÓ \(\frac{40}{90},\frac{41}{90}\)

VÂY 2 PHÂN SÓ Ở GIỮA \(\frac{13}{30},\frac{14}{30}\)LÀ \(\frac{40}{90},\frac{41}{90}\)

 TA THẤY:\(\frac{22}{30}=\frac{66}{90},\frac{33}{30}=\frac{99}{90}\)

TỰ LÀM

a) \(3:\frac{6}{7}=3\times\frac{7}{6}=\frac{21}{6}\)

b) \(\frac{5}{9}:5=\frac{5}{9}:\frac{5}{1}=\frac{5}{9}\times\frac{1}{5}=\frac{5}{45}=\frac{1}{9}\)

c) \(5:\frac{20}{21}=5\times\frac{21}{20}=\frac{105}{20}=\frac{21}{4}\)

d) \(\frac{3}{7}:9=\frac{3}{7}:\frac{9}{1}=\frac{3}{7}\times\frac{1}{9}=\frac{3}{63}=\frac{1}{21}\)

ủng hộ tớ nha

3:6/7=3x7/6=21/6

5/9:5=5/9x1/5=(5)/(9x5)=5/45=1/9

5:20/21=5x21/20=105/20=21/4

3/7:9=3/7x1/9=(3)/(7x9)=3/63=1/21

k minh nha

sông đáy 

tk mk nha

sông Đáy

a) 3/5:3/4=3/5x4/3=(3x4)/(5x3)=12/15=4/5

b)2/5:3/10=2/5x10/3=(2x10)/(5x3)=20/15=4/3

c)9/8:3/4=9/8x4/3=(9x4)/(8x3)=36/32=9/8

d)1/4:1/2=1/4x2=2/4=1/2

e)1/8:1/6=1/8x6=6/8=3/4

g)1/5:1/10=1/5x10=10/5=2

a) 3/5 : 3/4 = 4/5

b) 2/5 : 3/10 = 4/3

c) 9/8 : 3/4 = 3/2

d)  1/4 : 1/2 = 1/2

e) 1/8 : 1/6 = 3/4

g) 1/5 : 1/10 = 2

tk tớ nha

 = 5/6  x  6/7 x 7/8 x 8/9 x 9/10 

= 5/10

= 1/2

đúng 100% luôn bạn nhé

\(\left(1-\frac{1}{6}\right)\times\left(1-\frac{1}{7}\right)\times\left(1-\frac{1}{8}\right)\times\left(1-\frac{1}{9}\right)\times\left(1-\frac{1}{10}\right)\)

\(=\frac{5}{6}\times\frac{6}{7}\times\frac{7}{8}\times\frac{8}{9}\times\frac{9}{10}\)

\(=\frac{5\times6\times7\times8\times9}{6\times7\times8\times9\times10}\)

\(=\frac{5}{10}=\frac{1}{2}\)

Câu 3 : (mình giải theo phương trình bạn nhé)
Tóm Tắt 

Cr: 20
Cd: x
Chu vi: 3x (chu vi bằng 3 lần chiều dài, cd=x => Chu vi= 3x)
 

Gọi x là chiều dài hcn khi đó:

-Chu vi của hcn là 3x

Theo đề bài ta có phương trình: (Cvi hình chữ nhật = (d+r).2)
=> (20+x).2 = 3x
<=> 40+2x = 3x

<=> 2x-3x = -40 
<=> -x= -40

x= 40
 

a) \(\frac{1}{5}:\frac{2}{15}=\frac{1}{5}\times\frac{15}{2}\) 

                  \(=\frac{15}{10}=\frac{3}{2}\)

b)\(\frac{3}{7}:\frac{9}{14}=\frac{3}{7}\times\frac{14}{9}\)

                \(=\frac{42}{63}=\frac{2}{3}\)

c) \(\frac{7}{12}:\frac{21}{24}=\frac{7}{12}\times\frac{24}{21}\)

                    \(=\frac{168}{252}=\frac{2}{3}\)

d) \(\frac{9}{13}:\frac{27}{26}=\frac{9}{13}\times\frac{26}{27}\)

                   \(=\frac{234}{351}=\frac{2}{3}\)

k nha

A/ 15/10 = 3/2

B/ 42/63 = 2/3

C/ 168/252 = 2/3

D/ 234/351 = 2/3

\(\frac{42x32}{12x14x16}=\frac{\left(2x3x7\right)x\left(2x2x8\right)}{\left(3x2x2\right)x\left(2x7\right)x\left(2x8\right)}=\frac{1}{2}\)

42 nhân 32/12 nhân 14 nhân 16=1344/2688

rút gọn phân số 1344/2688=28/51

kích cho mình nha