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

bạn viết cái này nó dễ hơn đó 

\(a,\dfrac{2}{7}+\dfrac{5}{7}.\dfrac{7}{10}-\dfrac{1}{14}\)

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

\(=\dfrac{1}{7}.\left(2+\dfrac{35}{10}-\dfrac{1}{2}\right)\)

\(=\dfrac{1}{7}.\left(\dfrac{4}{2}+\dfrac{7}{2}-\dfrac{1}{2}\right)\)

\(=\dfrac{1}{7}.5=\dfrac{5}{7}\)

\(b,\left(3\dfrac{1}{2}-\dfrac{2}{3}\right).\dfrac{7}{34}-\dfrac{5}{34}\)

\(=\left(\dfrac{7}{2}-\dfrac{2}{3}\right).\dfrac{7}{34}-\dfrac{7}{34}.\dfrac{5}{7}\)

\(=\dfrac{7}{34}.\left(\dfrac{17}{6}-\dfrac{5}{7}\right)\)

\(=\dfrac{7}{34}.\dfrac{89}{42}=\dfrac{89}{204}\)

a: =2/7-1/14+5/10

=2/7-1/14+1/2

=4/14-1/14+7/14

=10/14=5/7

b: =(7/2-2/3)*7/34-5/34

\(=\dfrac{21-4}{6}\cdot\dfrac{7}{34}-\dfrac{5}{34}\)

\(=\dfrac{7}{6}\cdot\dfrac{1}{2}-\dfrac{5}{34}=\dfrac{7}{12}-\dfrac{5}{34}=\dfrac{89}{204}\)

bạn ghi lại đề đi bạn! Khó hiểu quá!

a) 1/2 + 3/4 - (3/4 - 4 - 5)

= 1/2 + 3/4 - 3/4 + 4 + 5

= (3/4 - 3/4) + (4 + 5) + 1/2

= 0 + 9 + 1/2

= 19/2

b) [9/16 + 8/(-27)] - (19/27- 7/16 - 2)

= 9/16 - 8/27 - 19/27 + 7/16 + 2

= (9/16 + 7/16) + (-8/27 - 19/27) + 2

= 1 - 1 + 2

= 2

c) -5/8 . [4/9 + 7/(-12)]

= -5/8 . (-5/36)

= 25/288

d) 7/10 . (-3/5) + 7/10 . (-2/5) - (-3/10)

= 7/10 . (-3/5 - 2/5) + 3/10

= 7/10 . (-1) + 3/10

= -2/5

e) -3/7 . 5/9 + 4/9 . (-3/7) + 2 3/7

= -3/7 . (5/9 + 4/9) + 17/7

= -3/7 . 1 + 17/7

= 2

f) 8 2/7 - (3 4/9 + 4 2/7)

= 8 + 2/7 - 3 - 4/9 - 4 - 2/7

= (8 - 3 - 4) + (2/7 - 2/7) - 4/9

= 1 - 4/9

= 5/9

h) 3.(-1/2)² - (4/5 + 8/15) : 5/6

= 3.1/4 - 4/3 : 5/6

= 3/4 - 8/5

= -17/20

DAI QUA . 

Bài 1: 

a: x+1/2=5/6

nên x=5/6-1/2=1/3

b: x+1/4=3/4

nên x=3/4-1/4=2/4=1/2

c: x+3/10=1/2

nên x=1/2-3/10=5/10-3/10=1/5

d: x+1/4=3/8

nên x=3/8-1/4=3/8-2/8=1/8

TOT LAM

\(\frac{-4}{7}+\left(\frac{-2}{3}+\frac{4}{7}\right)\)

\(=\frac{-4}{7}+\frac{-2}{3}+\frac{4}{7}\)

\(=\left(\frac{-4}{7}+\frac{4}{7}\right)+\frac{-2}{3}\)

\(=0+\frac{-2}{3}=\frac{-2}{3}\)

~ Hok tốt ~

\(\frac{-3}{10}.\frac{5}{12}+\frac{-3}{10}.\frac{7}{12}+5\frac{3}{10}\)

\(=\frac{-3}{10}.\frac{5}{12}+\frac{-3}{10}.\frac{7}{12}+\frac{53}{10}\)

\(=\frac{-3}{10}.\left(\frac{5}{12}+\frac{7}{12}\right)+\frac{53}{10}\)

\(=\frac{-3}{10}.1+\frac{53}{10}\)

\(=\frac{-3}{10}+\frac{53}{10}=\frac{50}{10}=5\)

~ Hok tốt ~

a]11/10 

b]13/56

c]9/8

d]7/12

tick cho mình nha

a,2/5+7/10=11/10 b,6/7-5/8=13/56 c,3/5 x 15/8=9/8 d,1/4:3/7=7/12 HT

bằng 7/12 nha bn