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ụa má ko chúc mình , chê nha má :))

a ) 2 3 . 4 5 = 8 15 b ) − 3 4 . 8 − 5 = 6 5 c ) 12 5 . − 6 − 8 = 9 5

a) 2 + 4/7=18/7

b)5/6-3/5=7/30

c)3/4 x 5/6=5/12

d)8/5 : 8/7=7/5

a) 2 + 4/7 = \(\dfrac{14}{7}+\dfrac{4}{7}=\dfrac{18}{7}\)

b)5/6-3/5= \(\dfrac{25}{30}-\dfrac{18}{30}=\dfrac{7}{30}\)

c)3/4 x 5/6= \(\dfrac{5}{8}\)

d)8/5 : 8/7= \(\dfrac{8}{5}x\dfrac{7}{8}=\dfrac{56}{40}=\dfrac{7}{5}\)

`a, 2/3 + 1/5 . 10/7`

`= 2/3 + 10/35`

`=2/3 +2/7`

`=14/21 + 6/21`

`=20/21`

`b, 2/7 + 5/7 . 14/25`

`=  2/7 +2/5`

`= 10/35+14/35`

`= 24/35`

`c, 7/12 - 27/7 . 1/18`

`= 7/12 - 3/14`

`= 31/84`

`d, 3/10 . (-5/6) - 1/8`

`= -1/4 -1/8`

`= -2/8 -1/8`

`= -3/8`

a)

\(\dfrac{2}{3}+\dfrac{1}{5}.\dfrac{10}{7}\)

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

\(=\dfrac{14}{21}+\dfrac{6}{21}\)

\(=\dfrac{20}{21}\)

b)

\(\dfrac{2}{7}+\dfrac{5}{7}.\dfrac{14}{25}\)

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

\(=\dfrac{10}{35}+\dfrac{14}{35}\)

\(=\dfrac{24}{35}\)

c)

\(\dfrac{7}{12}-\dfrac{27}{7}.\dfrac{1}{18}\)

\(=\dfrac{7}{12}-\dfrac{3}{14}\)

\(=\dfrac{98}{168}-\dfrac{36}{168}\)

\(=\dfrac{31}{84}\)

d)

\(\dfrac{3}{10}.\left(-\dfrac{5}{6}\right)-\dfrac{1}{8}\)

\(=-\dfrac{1}{4}-\dfrac{1}{8}\)

\(=-\dfrac{2}{8}-\dfrac{1}{8}\)

\(=\dfrac{-3}{8}\)

B. \(\dfrac{7}{5}\)

Câu hỏi của Thị Kim Vĩnh Bùi - Toán lớp 8 - Học toán với OnlineMath

Ở link trên đã tìm đc các giá trị của a, b, c, d thay vào tìm đc M = 0.

Chọn A

A