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

= 10 + 10 + 10 + 10 + 5

= 45

(1+9)+(2+8)+(3+7)+(4+6)+5
=10 + 10 + 10 + 10
=40

bài2:Tìm y:

a)y+253=1420                                 b)y-2316=902
y=1420-253                                        y=902+2316
y=1167                                               y=3218

bài3:Tính:

2754:9=306                    5089:7=727                   3675:5=735                   2010:6=335

2754x9=24786               5089x7=35623              3675x5=18375             2010x 6=12060

[1+19]+[4+16]+[7+13]+[22+28]+10+25=

20+20+20+50+35=145

y+253=1420

y        =1420-253

y        =1267

y-2316=902

y         =902+2316

y           =3218

(6/7-5/7)+(4/7-3/7)+(2/7-1/7)

=1+1+1

=3

milk nha

Giải sai rồi. Tính sao ra 1 là thấy nể quá :)

Nhóm như bạn đó nhưng kết quả phải là:

\(=\frac{1}{7}+\frac{1}{7}+\frac{1}{7}=\frac{1}{7}\times3=\frac{3}{7}\)

A = \(\dfrac{1}{2}\)+ \(\dfrac{1}{3}\)+ \(\dfrac{1}{4}\)+ \(\dfrac{1}{2}\)+ \(\dfrac{2}{3}\)+ \(\dfrac{3}{4}\)

A = ( \(\dfrac{1}{2}\)+ \(\dfrac{1}{2}\)) + ( \(\dfrac{1}{4}\)+\(\dfrac{3}{4}\)) +( \(\dfrac{1}{3}\)+ \(\dfrac{2}{3}\))

A = 1 + 1 + 1

A = 3

B = ( \(\dfrac{3}{4}\) + \(\dfrac{5}{7}\)+ \(\dfrac{16}{64}\)+ \(\dfrac{2}{7}\)) - 2

B = ( \(\dfrac{3}{4}\)+ \(\dfrac{1}{4}\)) + ( \(\dfrac{5}{7}\)+ \(\dfrac{2}{7}\)) - 2

B = 1 + 1 - 2

B = 2 - 2

B = 0

\(\dfrac{1}{7}+\dfrac{2}{7}+\dfrac{3}{7}+\dfrac{4}{7}+\dfrac{5}{7}+\dfrac{6}{7}\)

\(=\dfrac{1+2+3+4+5+6}{7}=3\)

\(\dfrac{1}{7}+\dfrac{2}{7}+\dfrac{3}{7}+\dfrac{4}{7}+\dfrac{5}{7}+\dfrac{6}{7}\)

\(=\left(\dfrac{1}{7}+\dfrac{6}{7}\right)+\left(\dfrac{2}{7}+\dfrac{5}{7}\right)+\left(\dfrac{3}{7}+\dfrac{4}{7}\right)\)

\(=1+1+1\)

\(=3\)

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`

Tham khảo nhé bạn :))

bbbbb

a)  739 x 2  +  739 +  739 x 3 + 739 x 4

=  739  x  2  + 739 x 1 + 739 x 3 + 739 x 4

=   739  x  ( 2 + 1 + 3 + 4 )

=   739  x    10

=    7390

b)  \(\frac{1}{7}\) +  \(\frac{2}{7}\) +  \(\frac{3}{7}\)+  \(\frac{4}{7}\) +  \(\frac{5}{7}\) +  \(\frac{6}{7}\)

=    (   \(\frac{1}{7}\) +   \(\frac{6}{7}\) )  +  (   \(\frac{2}{7}\) +  \(\frac{5}{7}\) )  +  (  \(\frac{3}{7}\)+   \(\frac{4}{7}\)  )

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

=                             \(3\)

~ Hok T ~

đ/s là 287 nha bạn

`3/7+2/5+4/7`

`=(3/7+4/7)+2/5`

`=1+2/5`

`=5/5+2/5`

`=7/5`

`20/34+4/9+7/17`

`=(20/34+7/17)+4/9`

`=(20/34+14/34)+4/9`

`=34/34+4/9`

`=1+4/9`

`=9/9+4/9`

`=13/9`

`48xx2+96+48xx6`

`=48xx2+48xx2+48xx6`

`=48xx(2+2+6)`

`=48xx10`

`=480`

câu thứ hai thì làm như này em nhé:

    \(\dfrac{20}{34}\) + \(\dfrac{4}{9}\) + \(\dfrac{7}{17}\)

= (\(\dfrac{20}{34}\) + \(\dfrac{7}{17}\)) + \(\dfrac{4}{9}\)

=  (\(\dfrac{10}{17}\) + \(\dfrac{7}{17}\)) + \(\dfrac{4}{9}\)

= 1 + \(\dfrac{4}{9}\)

= \(\dfrac{13}{9}\)