1/2x1/3+1/3x1/4+1/4x1/5+1/5x1/6+1/6x1/7+1/7x1/8+1/8x1/9

=7/18

a) 3/2:9/4+21/8

= 3/2 x 4/9 + 21/8

=12/18 + 21/8

= 2/3 + 21/8 = 16/24 + 63/24 = 79/24

b) 3/10+5/2x1/3

=3/10 + 5/6

= 9/30 + 25/30 = 34/30 = 17/15

c) 8/15:3/11+2/15:2/11

= 8/15x11/3 + 2/15x11/2

= 88/45 + 22/30

= 88/45 + 11/15 = 88/45 + 33/45 = 121/45

d) 19/5-11/4:9/8

= 19/5 - 11/4x8/9

= 19/5 - 88/36

= 19/5 - 22/9 = 171/45 - 110/45 = 61/45

e) 33/7:11/6+37/15x21/74

= 33/7x6/11 + 7/10

= 198/77 + 7/10 = 1980/770 + 1386/770 = 153/35

a) 3/2:9/4+21/8

= 3/2 x 4/9 + 21/8

=12/18 + 21/8

= 2/3 + 21/8 = 16/24 + 63/24 = 79/24

b) 3/10+5/2x1/3

=3/10 + 5/6

= 9/30 + 25/30 = 34/30 = 17/15

c) 8/15:3/11+2/15:2/11

= 8/15x11/3 + 2/15x11/2

= 88/45 + 22/30

= 88/45 + 11/15 = 88/45 + 33/45 = 121/45

d) 19/5-11/4:9/8

= 19/5 - 11/4x8/9

= 19/5 - 88/36

= 19/5 - 22/9 = 171/45 - 110/45 = 61/45

e) 33/7:11/6+37/15x21/74

= 33/7x6/11 + 7/10

= 198/77 + 7/10 = 1980/770 + 1386/770 = 153/35

1/2x1/3+1/3-1/4+1/4x1/5

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

=1/2-1/5

=3/10. (1/2x1/3= 1/2x3) 

1/2x1/3+1/3-1/4+1/4x1/5 = 1/2-1/3+1/3-1/4+1/4-1/5 =1/2-1/5 =3/10. (1/2x1/3= 1/2x3)

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

19/20x2/100+19/20x2/100

= [19/20+19/20]x2/100

= 38/20x2/100

= 19/500

75/76x102/100-75/76x2/100

= [102/100-2/100]x75/76

= 1x75/76

= 75/76

3x7/10+7/10x5+2x7/10

= [3+5+2]x7/10

= 10x7/10

= 7

giá trị biểu thức 

2/5+2/3x3/4

= 2/5+1/6

= 17/30

1/2x1/3-1/8

= 1/6-1/8

= 1/24

[1/2+1/3]:3/9

= 5/6:3/9

= 5/2

                       nhớ tick cho tớ nhé

rùi đó

\(\left(\frac{5}{12}+\frac{1}{2}.\frac{1}{3}\right):\left(2.\frac{1}{3}-1.\frac{5}{12}\right)\)

\(=\left(\frac{5}{12}+\frac{1}{6}\right):\left(\frac{2}{3}-\frac{5}{12}\right)\)

\(=\frac{7}{12}:\frac{1}{4}\)

\(=\frac{7}{3}\)

_Chúc bạn học tốt_

5/8 + 1/8 = 6/8 = 3/4

5/2 - 2 = 1/2

=3/4
=1/2

a. 5/8+1/2x1/4=5/8+1/8=6/8=3/4

b.5/2-1/4:1/8=5/2-(1/4✖8)=5/2-2=5/2-4/2=1/2

Đề bài 

= ( 5/12 +    1/6 ) : (    2/3 - 1/12 ) 

= ( 5/12 + 2/12 ) :   ( 8/12 - 1/12 ) 

= 7/12 : 7/12 

= 1 

K Trắng nha .

=1 nha