a,3/5*7/9+11/9*3/5-3/10=3/5*(7/9+11/9)-3/10

=3/5*18/9-3/10

=3/5*2-3/10

=6/5-3/10

=12/10-3/10

=9/10

b,14/13:1/2+3/13*2-2*7/13=14/13*2+3/13*2-2*7/13

=2*(14/13+3/13-7/13)

=2*10/13

=20/13

a/ ( 7/9 + 11/9 ) x 3/5 - 3/10

 =    2 x 3/5 - 3/10

=    6/5  - 3/10

 =    9/10

b/ 14/13 :  1/2 + 3/13 x 2 - 2 x 7/13

14/13 x 2/1 + 3/13 x 2 - 2 x 7/13

2 x ( 14/13 + 3/13 - 7/13 )

2 x 10/13

20/13

1*3+5*7+9*11+...+99*101

=(1/11+10/11)+(2/11+9/11)+(3/11+8/11)+(4/11+7/11)+(5/11+6/11)

=11/11+11/11+11/11+11/11+11/11

=1+1+1+1+1

=5

=1+2+3+4+5+6+7+8+9+10 trên 11

= (1+9)+(2+8)+3+7)+(4+6)+5+10 trên 11

=10+10+10+10+10+5 trên 11

=10x5+5 trên 11

=50+5 trên 11

=55/11

=5

trên có nghĩa là (tất cả) phần 11 nha.

1/11+2/11+3/11+4/11+5/11+6/11+7/11+8/11+9/11+10/11

=(1/11+10/11)+(2/11+9/11)+(3/11+8/11)+(4/11+7/11)+(5/11+6/11)

=1+1+1+1+1

=5

chúc bạn học tốt!

\(\frac{9}{10}\)+\(\frac{7}{9}\)+\(\frac{5}{8}\)+\(\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)

\(=\left(\frac{9}{10}+\frac{1}{10}\right)+\left(\frac{7}{9}+\frac{2}{9}\right)+\left(\frac{5}{8}+\frac{3}{8}\right)\)\(+\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

\(=1+1+1+1+1\)

\(=5\)

9/10 + 7/9 + 5/8 + 3/7 + 3/5 + 2/5 + 4/7 + 3/8 + 2/9 + 1/10

= ( 9/10 + 1/10 ) + ( 7/9 + 2/9 ) + ( 5/8 + 3/8 ) + ( 3/7 + 4/7 ) + ( 3/5 + 2/5 )

= 1 + 1 + 1 + 1 + 1

= 5

= (9/10+ 1/10 )+(7/9 + 2/9)+( 5/8 +3/8)+(3/5 +2/5)

=1+1+1+1=4

\(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)

= \(\left(\frac{9}{10}+\frac{1}{10}\right)+\left(\frac{7}{9}+\frac{2}{9}\right)+\left(\frac{5}{8}+\frac{3}{8}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

= \(\frac{10}{10}+\frac{9}{9}+\frac{8}{8}+\frac{7}{7}+\frac{5}{5}\)

= \(1+1+1+1+1\)

= \(1\times5\)

= \(5\)

Gọi A là tổng của 9/10 + 7/9 + 5/8 + 3/7 + 3/5 + 2/5 + 4/7 + 3/8 + 2/9 + 1/10, ta có :

A = 9/10 + 7/9 + 5/8 + 3/7 + 3/5 + 2/5 + 4/7 + 3/8 + 2/9 + 1/10

A = (9/10 + 1/10) + (7/9 + 2/9) + (5/8 + 3/8) + (3/7 + 4/7) + (3/5 + 2/5)

A = 1 + 1 + 1 + 1 + 1

A = 5

Ta có \(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)

\(=\left(\frac{9}{10}+\frac{1}{10}\right)+\left(\frac{7}{9}+\frac{2}{9}\right)+\left(\frac{3}{8}+\frac{5}{8}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{2}{5}+\frac{3}{5}\right)\)

\(=1+1+1+1+1\)

\(=5\)

1 + 2 + 3 + 4 + 5 + 6 + 7 + 8 + 9 + 10 + 11 + 12 

= ( 1 + 12 ) + ( 2 + 11 ) + ( 3 + 10 ) + ( 4 + 9 ) + ( 5 + 8 ) + ( 6 + 7 ) 

=     13         +     13       +     13       +      13     +    13      + 13

=               13 x 6 

=                 78

sai thui

1+2+3+4+5+6+7+8+9+10+11+12

=(1+9)+(2+8)+(3+7)+(4+6)+(5+10)+(11+12)

=10+10+10+10+15+23

=10×4+15+23

=40+15+23

=55+23

=78

ủng hộ nha có gì sai sót mong bạn thông cảm cho !!!

1 + 2 + 3 + 4 +5 + 6 + 7 + 8 + 9 + 10 +11 + 12

= ( 12 + 8 ) + ( 11 + 9 ) + ( 7 + 3 ) + ( 6 + 4 ) + ( 10 + 2 + 3 ) + 1

Mình cũng không biết nữa !

\(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)\(=\frac{9}{10}+\frac{1}{10}+\frac{7}{9}+\frac{2}{9}+\frac{5}{8}+\frac{3}{8}+\frac{3}{7}+\frac{4}{7}+\frac{3}{5}+\frac{2}{5}\)

\(=\left[\frac{9}{10}+\frac{1}{10}\right]+\left[\frac{7}{9}+\frac{2}{9}\right]+\left[\frac{5}{8}+\frac{3}{8}\right]+\left[\frac{3}{7}+\frac{4}{7}\right]+\left[\frac{3}{5}+\frac{2}{5}\right]\)

\(=1+1+1+1+1\)

   \(=5\)

\(\frac{9}{10}+\frac{7}{9}+\frac{5}{8}+\frac{3}{7}+\frac{3}{5}+\frac{2}{5}+\frac{4}{7}+\frac{3}{8}+\frac{2}{9}+\frac{1}{10}\)

= \(\left(\frac{9}{10}+\frac{1}{10}\right)+\left(\frac{7}{9}+\frac{2}{9}\right)+\left(\frac{5}{8}+\frac{3}{8}\right)+\left(\frac{3}{7}+\frac{4}{7}\right)+\left(\frac{3}{5}+\frac{2}{5}\right)\)

= 1 + 1 + 1 + 1 + 1

= 5

=1+1+1+1+1

=5

ai cứu với ạ

ko 

có chết đâu mà phải cứu

1,

a,=4/7:4/9.3

=9/7.3

=27/7

b,=(7/11+4/11).5/6

=1.5/6

=5/6

`(6/7-2/7):4/9xx3=4/7xx9/4xx3=[4xx9xx3]/[7xx4]=27/7`

`7/11xx5/6+4/11xx5/6=(7/11+4/11)xx5/6=11/11xx5/6=5/6`