Câu 1

\(a,\dfrac{2}{5}\times x=4\\ x=4:\dfrac{2}{5}=10\\ b,7:x=\dfrac{4}{5}\\ x=\dfrac{4}{5}\times7=\dfrac{28}{5}\) 

Câu 2

\(=\left(\dfrac{5}{9}+\dfrac{4}{9}\right)\times\dfrac{8}{17}=1\times\dfrac{8}{17}=\dfrac{8}{17}\)

Câu 1: Tìm x:

a)  2/5× x = 4

x=4 : 2/5

x=10

 8/7: x =4/5 

x=8/7:4/5

x=10/7

Câu 2: Tính bằng cách thuận tiện nhất

5/9× 8/17 + 4/9 × 8/17

=(5/9+4/9)x8/17

=1x8/17=8/17

\(5/9× 8/17 + 4/9 × 8/17 =>(5/9+4/9)×8/17 =>1 ×8/17=8/17\)

bài 1

\(\frac{2}{5}+x=4\)                          ,                    \(\frac{8}{7}:x=\frac{4}{5}\)

\(\Rightarrow\)\(x=4-\frac{2}{5}\)              ,               \(\Rightarrow\)\(x=\frac{8}{7}:\frac{4}{5}\)

\(\Rightarrow\)\(x=\frac{18}{5}\)                      ,             \(\Rightarrow\) \(x=\frac{10}{7}\)

tính cách thuận  tiện là  dấu = là x vì viết nhầm

1) Ta có: \(\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{7}{25}\cdot\dfrac{5}{7}\right)\)

\(=\left(\dfrac{3}{4}\cdot\dfrac{5}{97}+\dfrac{1}{9}\cdot\dfrac{13}{47}\right)\cdot\left(\dfrac{1}{5}-\dfrac{1}{5}\right)\)

=0

2) Ta có: \(\dfrac{8}{17}\cdot\dfrac{4}{15}+\dfrac{8}{17}\cdot\dfrac{22}{15}-\dfrac{8}{15}\cdot\dfrac{9}{17}\)

\(=\dfrac{8}{17}\left(\dfrac{4}{15}+\dfrac{22}{15}-\dfrac{9}{15}\right)\)

\(=\dfrac{8}{17}\cdot\dfrac{15}{15}=\dfrac{8}{17}\)

3) Ta có: \(\dfrac{2021}{2}\cdot\dfrac{1}{3}+\dfrac{4042}{4}\cdot\dfrac{1}{5}+\dfrac{6063}{3}\cdot\dfrac{22}{15}\)

\(=\dfrac{2021}{2}\left(\dfrac{1}{3}+\dfrac{1}{5}\right)+2021\cdot\dfrac{22}{15}\)

\(=\dfrac{2021}{2}\cdot\dfrac{8}{15}+\dfrac{2021}{2}\cdot\dfrac{44}{15}\)

\(=\dfrac{2021}{2}\cdot\dfrac{52}{15}\)

\(=\dfrac{52546}{15}\)

4) Ta có: \(\dfrac{4}{7}\cdot\dfrac{2}{13}+\dfrac{8}{13}:\dfrac{7}{4}+\dfrac{4}{7}:\dfrac{13}{2}+\dfrac{4}{7}\cdot\dfrac{1}{13}\)

\(=\dfrac{4}{7}\left(\dfrac{2}{13}+\dfrac{8}{13}+\dfrac{2}{13}+\dfrac{1}{13}\right)\)

\(=\dfrac{4}{7}\)

1) Tính biểu thức:

= (5/9 + 4/9) x 8/17

= 1 x 8/17

= 8/17

=(5/9+4/9).8/17

=1.8/17

=8/17

5/9 nhân 8/17+4/9 nhân 8/17

=[5/9+4/9] nhân 8/17

=1 nhân 8/17

8/17

a) 3/7+5/2+4/7

=(3/7+4/7)+5/2

=1+5/2

=7/2

b)6/8+4/5+1/4

=(6/8+1/4)+4/5

=1+4/5

=9/5

đến đó thôi mệt quá

a; \(\dfrac{3}{7}\) + \(\dfrac{5}{2}\) + \(\dfrac{4}{7}\)

= (\(\dfrac{3}{7}+\dfrac{4}{7}\)) + \(\dfrac{5}{2}\)

= 1 + \(\dfrac{5}{2}\)

= \(\dfrac{2}{2}+\dfrac{5}{2}\)

=  \(\dfrac{7}{2}\)

b; \(\dfrac{6}{8}\) + \(\dfrac{4}{5}\) + \(\dfrac{1}{4}\) 

= \(\dfrac{1}{4}\) + \(\dfrac{4}{5}\) + \(\dfrac{1}{4}\)

= (\(\dfrac{1}{4}\) + \(\dfrac{1}{4}\)) + \(\dfrac{4}{5}\)

= \(\dfrac{2}{4}\) + \(\dfrac{4}{5}\)

= \(\dfrac{1}{2}\) + \(\dfrac{4}{5}\)

= \(\dfrac{5}{10}\) + \(\dfrac{8}{10}\)

= \(\dfrac{13}{10}\)

c; \(\dfrac{21}{34}\) + \(\dfrac{4}{9}\) + 7 + 17

= (\(\dfrac{21}{34}\) + \(\dfrac{4}{9}\)) + (7 + 17)

= \(\dfrac{325}{306}\) + 24

= \(\dfrac{7669}{306}\)

miu miu cai dau may e

nho k tao khong an dap

BÀI NÀY DỄ ỢT VỚI MK NHƯNG TRÌNH BÀY ĐẦY ĐỦ THÌ MK...CHỊU +_+

a,\(60\times\left(\frac{7}{12}+\frac{4}{15}\right)\)\(=\frac{60\times7}{12}+\frac{60\times4}{15}\)

                                         \(=\frac{12\times5\times7}{12}+\frac{15\times4\times4}{15}\)

                                         \(=5\times7+4\times4\)

                                          \(=35+16\)                                            

                                            \(=51\)

b, \(\frac{1}{2}\times\frac{2}{3}\times\frac{3}{4}\times...\times\frac{8}{9}\)\(=\frac{1\times2\times3\times4\times5\times6\times7\times8}{2\times3\times4\times5\times6\times7\times8\times9}\)

                                                        \(=\frac{1}{9}\)

ai vhat nhìu thì kt bn với mình nha

trả lời mình đi

Tao mách cô mày hỏi bài thi nhá

`1/2 xx 2/3 xx 3/4 xx 4/5 xx 5/6 xx 6/7 xx 7/8 x 8/9`

`= [1 xx 2 xx 3 xx 4 xx 5 xx 6 xx 7 xx 8]/[2 xx 3 xx 4 xx 5 xx 6 xx 7 xx 8 xx 9]`

`= 1/9`

HT~