`a)1/10 + 2/10 + 3/10 + 4/10 + 5/10 + 6/10 + 7/10 + 8/10 + 9/10`

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

`=10/10 + 10/10+10/10+10/10+1/2`

`=1+1+1+1+1/2`

`=2+2+1/2`

`=4+1/2`

`=8/2+1/2`

`=9/2`

__

`13,25:0,5+13,25:0,25+13,25:0,125+13,25×6`

`=13,25×1/(0,5)+13,25×1/(0,25)+13,25×1/(0,125)+13,25×6`

`=13,25×(1/(0,5)+1/(0,25)+1/(0,125)+6)`

`=13,25×(2+4+8+6)`

`=13,25×20`

`=265`

`#QiN`

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`

a) \(\dfrac{5}{7}\times\dfrac{5}{9}+\dfrac{4}{9}\times\dfrac{5}{7}\)

\(=\dfrac{5}{7}\times\left(\dfrac{4}{9}+\dfrac{5}{9}\right)\)

\(=\dfrac{5}{7}\times1\)

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

b) \(\dfrac{1}{10}+\dfrac{5}{9}+\dfrac{4}{9}+\dfrac{9}{10}-1\)

\(=\left(\dfrac{5}{9}+\dfrac{4}{9}\right)+\left(\dfrac{1}{10}+\dfrac{9}{10}-1\right)\)

\(=1+0\)

\(=1\)

c) \(\dfrac{5}{7}\times\dfrac{5}{9}+\dfrac{4}{9}\times\dfrac{5}{7}+\dfrac{2}{7}\)

\(=\dfrac{5}{7}\times\left(\dfrac{5}{9}+\dfrac{4}{9}\right)+\dfrac{2}{7}\)

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

\(=1\)

d) \(\dfrac{2}{7}+\dfrac{2}{8}+\dfrac{1}{4}+\dfrac{1}{7}+\dfrac{4}{7}\)

\(=\left(\dfrac{2}{8}+\dfrac{1}{4}\right)+\left(\dfrac{2}{7}+\dfrac{1}{7}+\dfrac{4}{7}\right)\)

\(=\left(\dfrac{1}{4}+\dfrac{1}{4}\right)+1\)

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

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

e) \(\dfrac{4}{5}+\dfrac{3}{10}+\dfrac{2}{10}+0,7\)

\(=\dfrac{4}{5}+\dfrac{5}{10}+\dfrac{7}{10}\)

\(=\dfrac{4}{5}+\dfrac{12}{10}\)

\(=\dfrac{4}{5}+\dfrac{6}{5}\)

\(=\dfrac{10}{5}\)

\(=2\)

g) \(362\times728+326\times272\)

\(=326\times\left(728+272\right)\)

\(=326\times1000\)

\(=326000\) 

9/5 + 4/7 + 6/5 + 3/7

=  ( 9/5 + 6/5 ) + ( 4/7 + 3/7)

=            3        + 1

=        4

9/5 + 4/7 + 6/5 + 3/7 = (9/5 + 6/5) + (4/7 + 3/7)

= 15/5 + 7/7

= 3 + 1

= 4

1/2 x 45/33 x 1/9 x 11/6 = (1/2 x 1/9) x (45/33 x 11/6)

= 1/18 x 45/18

= 5/2

1/2 x 45/33 x 1/9 x 11/6

= (1/2 x 1/9) x (45/33 x 11/6)

= 1/18 x 45/18

= 5/2

Bài 2:

a: 2/6x5/3=10/18=5/9

b: 11/9x5/10=55/90=11/18

c: 3/9x6/8=1/3x3/4=1/4

d: 4/9x12/16=48/144=1/3

e: 25/15x6/7=5/3x6/7=30/21=10/7

f: 6/10x15/20=90/200=9/20

Bài 1

4/5 x 6/7= 24/35

2/9 x 1/2= 2/18= 1/9

1/2 x 8/3= 8/6= 4/3

7/9 x 6/5= 42/45= 14/15

8/7 x 5/9= 40/63

10/11 x 22/15= 220/165= 4/3

Bài 2

2/6 x 5/3= 1/3 x 5/3=5/9

11/9 x 5/10= 11/9 x 1/2= 11/18

3/9 x 6/8= 1/3 x 3/4 =3/12= 1/4

4/9 x 12/16= 4/9 x 3/4= 12/36= 1/3

25/15 x 6/7= 5/3 x 6/7= 30/21= 10/7

6/10 x 15/20= 3/5 x 3/4= 9/20

bài 1

4/5 x 6/7 = 24/35

2/9 x 1/2 = 1/9

1/2 x 8/3 = 4/3

7/9 x 6/5 = 14/15

8/7 x 5/9 = 14/15

8/7 x 5/9 = 40/63

10/11 x 22/15 = 4/3

Bài 2:

Sau 2 giờ con ốc sên bò được:

1/5+1/6=11/30(cây cột)

Sau 2 giờ thì con ốc sên còn phải bò:

1-11/30=19/30(cây cột)

a) 7,2 x 94,3 + 7,2 x 4,7 + 7,2

=7,2 x(94,3+4,7+1)

=7,2x100

=720

b)\(\dfrac{7}{9}\times\dfrac{2}{3}+\dfrac{7}{9}\times\dfrac{1}{3}=\dfrac{7}{9}\times\left(\dfrac{2}{3}+\dfrac{1}{3}\right)=\dfrac{7}{9}\times1=\dfrac{7}{9}\)

Bài 2:
a) x + 5,7 = 18,6 - 10,3
    x + 5,7 = 8,3
    x          = 8,3 - 5,7 
    x          = 3,6
b) 6,4 . x  = 5 . 3,2
    6,4 . x  = 16
    6,4 . x  = 16 : 6,4 
    6,4 . x  = 2,5

B1

a) 3/5 . 20/18 : 2/9 .1/15

= 3/5 . 20/18 . 9/2 .1/15

= (3/5 . 1/15) . (20/18 . 9/2)

= 1/25 . 5

= 1/5

b. (5/2 + 1/8) : (1 - 7/16)

= 21/8 : 9/16

= 21/8 . 16/9

= 14/3 

B2:

\(a.x+5,7=18,6-10,3\\ x=18,6-10,3-5,7\\ x=18,6-\left(10,3+5,7\right)\\ x=18,6-16\\ x=2,6\\ b.6,4\cdot x=5\cdot3,2\\ \left(3,2\cdot2\right)\cdot x=5\cdot3,2\\ x=\dfrac{5}{2}\cdot\left(3,2:3,2\right)\\ x=\dfrac{5}{2}\)

c) x + 2/4 = 15/9 + 3/36

x + 2/4 = 7/4

x = 7/4 - 2/4

x = 5/4

d) x . 4/3 = 15/3 - 22/6

 x . 4/3 = 4/3 

x = 4/3 :4/3

 x = 1

B4:

Gọi số đầu tiên là a

Vì tổng của 4 số tự nhiên liên tiếp  = 2010

=> a + (a+1) + (a+2) + (a+3) =2010

=> a4 + 6 = 2010

=> a4 = 2004

=> a = 501

Số thứ 2 là:

501 + 1 = 502

Số thứ 3 là:

502 + 1 = 503

Số thứ 4 là :

503 + 1 = 504