bài 7

a)232/105

b)11/6

c)23/36

nhân chia trc coiongj trừ sau nhé

= 91/35 + 20/35 - 101/105 = 111/35 - 101/105 = 232/105

b,=1/2.4/1 - 1/6 = 2 - 1/6 = 11/6

c, = 8/12 - 3/12 + 2/9 = 5/12 + 2/9 = 23/36

con bai 8 minh ko biet lam

BẠN VIẾT RÕ RÀNG RA NHÉ ~~^^

tên rõ hay

t

\(\dfrac{2}{5}\times\dfrac{1}{7}+\dfrac{2}{7}\times\dfrac{2}{5}\)

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

\(=\dfrac{2}{5}\times\dfrac{3}{7}\)

\(=\dfrac{6}{35}\)

\(x+\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}\)

\(x+\dfrac{1}{6}=\dfrac{3}{4}\)

\(x=\dfrac{9}{12}-\dfrac{2}{12}\)

\(x=\dfrac{7}{12}\)

\(\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{3}\right)\times\left(1-\dfrac{1}{4}\right)\times...\times\left(1-\dfrac{1}{2020}\right)+x=\dfrac{1}{2}\)

\(\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times...\times\dfrac{2019}{2020}+x=\dfrac{1}{2}\)

\(\dfrac{1}{2020}+x=\dfrac{1}{2}\)

\(x=\dfrac{1}{2}-\dfrac{1}{2020}\)

\(x=\dfrac{1010}{2020}-\dfrac{1}{2020}\)

\(x=\dfrac{1009}{2020}\)

\(\dfrac{2}{5}\times\dfrac{1}{7}+\dfrac{2}{7}\times\dfrac{2}{5}\)

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

\(=\dfrac{2}{5}\times\dfrac{3}{7}\)

\(=\dfrac{6}{35}\)

\(x+\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}\)

\(\Rightarrow\dfrac{1}{2}\times\dfrac{1}{3}=\dfrac{3}{4}-x\)

\(\Rightarrow\dfrac{3}{4}-x=\dfrac{1}{6}\)

\(\Rightarrow x=\dfrac{3}{4}-\dfrac{1}{6}=\dfrac{7}{12}\)

\(\left(1-\dfrac{1}{2}\right)\times\left(1-\dfrac{1}{3}\right)\times\left(1-\dfrac{1}{4}\right)\times...\times\left(1-\dfrac{1}{2020}\right)+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{2}\times\dfrac{2}{3}\times\dfrac{3}{4}\times...\times\dfrac{2019}{2020}+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1\times2\times3\times4\times...\times2019}{2\times3\times4\times5\times...\times2020}+x=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{1}{2020}+x=\dfrac{1}{2}\)

\(\Rightarrow x=\dfrac{1}{2}-\dfrac{1}{2020}=\dfrac{1009}{2020}\)

\(\frac{2}{3}\)x \(\frac{5}{8}\)x \(\frac{8}{15}\)= \(\frac{2}{3}\)x \(\frac{1}{15}\)= \(\frac{2}{45}\)

\(\frac{22}{5}\)x \(12\)x \(\frac{20}{40}\)= \(\frac{22}{5}\)x \(12\)x \(\frac{1}{2}\)= \(\frac{22}{5}\)x 6 = \(\frac{122}{5}\)

\(\frac{7}{2}\)x \(\frac{26}{7}\)x \(\frac{4}{13}\)= \(\frac{91}{7}\)x \(\frac{4}{13}\)

   [4\(\dfrac{1}{5}\) - 2\(\dfrac{2}{5}\)] x 8\(\dfrac{5}{6}\)

= [\(\dfrac{21}{5}\) - \(\dfrac{12}{5}\)] x \(\dfrac{53}{6}\)

= \(\dfrac{9}{5}\) x \(\dfrac{53}{6}\)

= \(\dfrac{159}{10}\)

   [5\(\dfrac{1}{3}\) - 2\(\dfrac{2}{3}\)]: \(\dfrac{3}{7}\)

= [\(\dfrac{16}{3}\) - \(\dfrac{8}{3}\)]: \(\dfrac{3}{7}\)

= \(\dfrac{8}{3}\) : \(\dfrac{3}{7}\)

= \(\dfrac{56}{9}\)

11 x 2 + 12 x 3 + 13 x 4 +...+ 1999 x 1000 + 1 

= 22 + 36 + 52 + ....+ 1999000 + 1 

đến đây thì chịu rồi nó không có quy luật 

ko thể tính câu nhé

11x2+12x3+13x4+...+1999x1000+1

=11x2+(11+1)x3+(11+2)x4+...+(11+1988)x1000+1

=11x2+11x3+3+11.4+8+...+11x1000+1988x1000+1

rút thừa số chung11 rồi tính tiếp

 k mình nha

\(\dfrac{15}{24}-\dfrac{3}{8}-\dfrac{1}{6}=\dfrac{5}{8}-\dfrac{3}{8}-\dfrac{1}{6}=\dfrac{1}{4}-\dfrac{1}{6}=\dfrac{1}{12}\)

\(\dfrac{7}{13}\cdot\dfrac{5}{24}\cdot\dfrac{39}{75}=\dfrac{39}{13}\cdot\dfrac{5}{75}\cdot\dfrac{7}{24}=3\cdot\dfrac{1}{15}\cdot\dfrac{7}{24}=\dfrac{35}{24}\)

`15/24-3/8-1/6`

`=15/24-9/24-4/24`

`=2/24`

`=1/12

d, `7/13 . 5/24 . 39/75`

`=(7.5.13.3)/(13.24.5.5.3)`

`=7/(24.5)`

`=7/120`

6 2/7  + 7 3/5 + 8 6/9 + 9 1/4 + 2/5 +  5/7 + 1/3  x 3/4 + 1967

= 44/7 + 38/5 + 78/9 + 37/4 + 2/5 + 5/7 + 1/3 + 1967

= ( 44/7 + 5/7 ) + ( 38/5 + 2/5 ) + ( 26/3 + 1/3 ) + ( 37/4 + 3/4 )  +1967

=  7 + 8 + 9 + 10  + 1967

= 15  + 9 + 10 + 1967

= 24 + 10 + 1967

= 34 + 1967 

= 2001

tính nhanh lớp 6 20 nhân 17-4 nhân 5 nhân 7