13/19 x 23/11 - 13/19 x 8/11 - 13/19 x 4/11

= 13/19 x (23/11 - 8/11 - 4/11)

= 13/19 x 1

= 13/19

\(\dfrac{13}{19}\times\dfrac{23}{11}-\dfrac{13}{19}\times\dfrac{8}{11}-\dfrac{13}{19}\times\dfrac{4}{11}\\ =\dfrac{13}{19}\times\left(\dfrac{23}{11}-\dfrac{8}{11}-\dfrac{4}{11}\right)\\ =\dfrac{13}{19}\times1=\dfrac{13}{19}\)

câu b, 20/5x7 + 20/7x9 + 20/ 9 x11 + ..... 20 / 33 x35

nhiều thế

sfdhg 

19/11 + ( 8/13 + 3/11 )

=( 19/11+3/11 )+8/13

=2+8/13

=26/13+8/13

=34/13

\(\dfrac{3}{5}+\dfrac{6}{11}+\dfrac{7}{13}+\dfrac{2}{5}+\dfrac{16}{11}+\dfrac{19}{13}\\ =\left(\dfrac{3}{5}+\dfrac{2}{5}\right)+\left(\dfrac{6}{11}+\dfrac{16}{11}\right)+\left(\dfrac{7}{13}+\dfrac{19}{13}\right)\\ =\dfrac{5}{5}+\dfrac{22}{11}+\dfrac{26}{13}\\ =1+2+2\\ =5\)

5

\(\frac{19}{11}+\left(\frac{8}{13}+\frac{3}{11}\right)=\frac{19}{11}+\frac{8}{13}+\frac{3}{11}\)

\(=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{8}{13}=2+\frac{8}{13}\)

\(=\frac{26}{13}+\frac{8}{13}=\frac{34}{13}\)

\(\frac{19}{11}+\left(\frac{8}{13}+\frac{3}{11}\right)\)

\(=\frac{19}{11}+\frac{8}{13}+\frac{3}{11}\)

\(=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{8}{13}\)

\(=2+\frac{8}{13}\)

\(=\frac{26}{13}+\frac{8}{13}=\frac{34}{13}\)

 bài làm rồi đi chép lại : )))?

a) ( 2/5 + 3/5) + 7/8

= 5/5 +7/8

= 1+ 7/8

=15/8 ( tính lại hộ mk nha, sợ ko đúng)

b)( 19/11 + 3/11 ) + 5/13

= 22/11 +5/13

= 2 + 5/13

= ...( bn tính nốt nha, vì mk ko có nháp ở đây )

k nha!!!

a) (2/5 + 7/8) + 3/5

= 2/5 + 7/8 + 3/5

= (2/5 + 3/5) + 7/8

= 1 + 7/8

= \(1\frac{7}{8}\)

b) 19/11 + (5/13 + 3/11)

= 19/11 + 5/13 + 3/11

= (19/11 + 3/11) + 5/13

= 2 + 5/13

= \(2\frac{5}{13}\)

\(a,\left(\frac{2}{5}+\frac{7}{8}\right)+\frac{3}{5}\)

\(=\frac{2}{5}+\frac{7}{8}+\frac{3}{5}\)

\(=\left(\frac{2}{5}+\frac{3}{5}\right)+\frac{7}{8}\)

\(=1+\frac{7}{8}\)

\(=\frac{15}{8}\)

\(b,\frac{19}{11}+\left(\frac{5}{13}+\frac{3}{11}\right)\)

\(=\frac{19}{11}+\frac{5}{13}+\frac{3}{11}\)

\(=\left(\frac{19}{11}+\frac{3}{11}\right)+\frac{5}{13}\)

\(=2+\frac{5}{13}\)

\(=\frac{31}{13}\)

giúp mình nha ,mìnhcaanf ngay câu trả lời , bạn nào trar lòi đúng mính k cho nha

1,x×1/2 + 3/2 × x = 4/5

X × (1/2 + 3/2 ) = 4/5

X × 2 = 4/5

4/5 : 2 = x

X = 2/5

2,

Số tròn trăm lớn nhất có 4 chữ số là :9900

Số lớn có 4 chữ số là : 9999

Tổng 2 số là :

9900 × 2 = 19 800

Số bé là : 

19 800 - 9 999 = 9 801 

3,

A)4/15 × 7/9 + 4/15 × 2/9 = 4/15 ×(7/9 +2/9)

                                               = 4/15 ×1 = 4/15

B)13 / 19 × 23 /11 - 13/19 × 8/11 - 13 / 19 × 4/11

=13/19 × (23/11 - 8/11 - 4/11)

= 13/19 × 1

= 13/19

\(\frac{13}{19}\cdot\frac{23}{11}-\frac{13}{19}\cdot\frac{8}{11}-\frac{13}{19}\cdot\frac{4}{11}=\frac{13}{19}\cdot\left(\frac{23}{11}-\frac{8}{11}-\frac{4}{11}\right)\)

\(=\frac{13}{19}\cdot1=\frac{13}{19}\)