a,=3/13.17/29.29/34

=3/13.1/2

=3/26

b,=(4/21+25/42).19/33

=11/14.19/33

=19/42

`a, = 3/13 xx (17/29 xx 29/34)`

`= 3/13 xx 1/2`

`= 3/26`.

`b, = 19/33(4/21 + 25/42)`

`= 19/33 xx ( 33/42 )`

`= 19/42`

$\frac{3}{13}\times \frac{17}{29})\times \frac{29}{34}$

     $=\frac{3}{13}\times \frac{17}{29}\times \frac{29}{34}$

     $=\frac{3\times 17\times 29}{13\times 29\times 34}$

     $=\frac{3\times 17\times 29}{13\times 29\times 2\times 17}$

     $=\frac{3}{13\times 2}$

     $=\frac{3}{26}$

toán lớp 5 khó thế bạn

5/13 x 11/19 + 11/19 x 21/13

=11/19 x ( 5/13 + 21/13 )

=11/19 x 26/13

=11/19 x 2

=22/19

a, 6/7*8/15*7/6*15/16

=(6/7*7/6)*(8/15*15/16)

=1*1/2

=1/2

b, Đề bài hơi sai

câu b mình sửa lại là 19/20 x 13/21 + 19/20 x 8/21

 36-4x9 = 36 - 36 = 0 Vì số nào nhân với 0 thì cũng bằng 0 nên phép tính đó bằng 0

=9,8 * 43 + 19 * 9,8 - 61 * 9,8

= 9,8 * (43+19-61)
=9,8 * (62-61)
=9,8*1

=9,8

\(9,8\times43+2\times19\times4,9-6,1\times9,8\)

\(=9,8\times43+19\times\left(2\times4,9\right)-6,1\times9,8\)

\(=9,8\times43+19\times9,8-61\times9,8\)

\(=9,8\times\left(43+19-61\right)\)

\(=9,8\times\left(62-61\right)\)

\(=9,8\times1\)

\(=9,8\)

19.9+9.(37+43)+9

=19.9+9.80+9

=9.(19+80+1)

=9.100

=900

`#Ya`

`= 19 × 9 + 9 × 80 + 9 × 1`

`= 9 × ( 19 + 80 + 1 )`

`= 9 × 100= 900`

2008 x 76 +2008 x 43 - 2008 x 19

= 2008 x (76+43-19)

= 2008 x 100

= 200800

2008 x 76 +2008 x 43 - 2008 x 19

=2008x(76+43-19)

=2008x100

=200800

\(=21\cdot1131=23751\)