\(\dfrac{5}{13}\times\dfrac{7}{11}+\dfrac{5}{13}\times\dfrac{2}{11}+\dfrac{8}{13}\times\dfrac{9}{11}\)

\(=\dfrac{5}{13}\times\left(\dfrac{7}{11}+\dfrac{2}{11}\right)+\dfrac{8}{13}\times\dfrac{9}{11}\)

\(=\dfrac{5}{13}\times\dfrac{9}{11}+\dfrac{8}{13}\times\dfrac{9}{11}\)

\(=\dfrac{9}{11}\times\left(\dfrac{5}{13}+\dfrac{8}{13}\right)\)

\(=\dfrac{9}{11}\times1\)

\(=\dfrac{9}{11}\)

a) \(20,23\times21+20,23\times80-20,23\)

\(=20,23\times\left(21+80-1\right)\)

\(=20,23\times100\)

\(=2023\)

\(\dfrac{5}{13}\) \(\times\) \(\dfrac{7}{11}\) + \(\dfrac{5}{13}\) \(\times\) \(\dfrac{2}{11}\) + \(\dfrac{8}{13}\) \(\times\) \(\dfrac{9}{11}\)

= \(\left(\dfrac{5}{13}\times\dfrac{7}{11}+\dfrac{5}{13}\times\dfrac{2}{11}\right)\)+ \(\dfrac{8}{13}\) \(\times\) \(\dfrac{9}{11}\)

= \(\dfrac{5}{13}\)\(\times\) (\(\dfrac{7}{11}\) + \(\dfrac{2}{11}\)) + \(\dfrac{8}{13}\) \(\times\) \(\dfrac{9}{11}\)

= \(\dfrac{5}{13}\) \(\times\) \(\dfrac{9}{11}\) + \(\dfrac{8}{13}\) \(\times\) \(\dfrac{9}{11}\)

= \(\dfrac{9}{11}\) \(\times\)( \(\dfrac{5}{13}\) +\(\dfrac{8}{13}\))

= \(\dfrac{9}{11}\) \(\times\) 1

= \(\dfrac{9}{11}\)

5/14*7/13*26/25

=7/14*5/25*26/13

=1/2*1/5*2

=1/5

5/14\(\times\)7/13\(\times\)26/25

=\(\frac{5\times7\times26}{14\times13\times25}\)(rút gọn)

=1/5

\(=\dfrac{5}{9}\times\dfrac{7}{4}+\dfrac{13}{9}\times\dfrac{7}{4}\\ =\left(\dfrac{5}{9}+\dfrac{13}{9}\right)\times\dfrac{7}{4}\\ =2\times\dfrac{7}{4}\\ =\dfrac{7}{2}\)

`5/9 : 4/7 + 13/9 xx 7/4`

`= 5/9 xx 7/4 + 13/9 xx 7/4`

`= ( 5/9 + 13/9 ) xx 7/4`

`= 18/9 xx 7/4`

`= 2 xx 7/4`

`=7/2` 

\(=\dfrac{5}{9}\times\dfrac{7}{4}+\dfrac{13}{9}\times\dfrac{7}{4}=\dfrac{7}{4}\times\left(\dfrac{5}{9}+\dfrac{13}{9}\right)=\dfrac{7}{4}\times2=\dfrac{14}{4}=\dfrac{7}{2}\)

a: =13/26*9/18*2/3=2/3*1/4=2/12=1/6

b: =44/22*5/15*3/2=2*1/3*3/2=2*1/2=1

a) 13 x 5 x 2 = 13 x (5 x 2)

                    =   13 x 10

                     = 130

5 x 2 x 34 = (5 x 2) x 34

                 = 10 x 34

                  = 340

b) 2 x 26 x 5 = (2 x 5) x 26

                      = 10 x 26

                     = 260

a) 13 x 5 x 2                       5 x 2 x 34                                  b) 2 x 26 x 5

= 13 x ( 5 x 2 )                    = ( 5 x 2 ) x 34                             = ( 2 x 5 ) x 26

= 13 x 10                             = 10 x 34                                    = 10 x 26

= 130                                   = 340                                          = 260

Chúc bạn học tốt!

^{_{13x5x2=(5x2)x13
           =10x13
           =130
5x2x34=10x34
           =340
2x26x5=(2x5)x26
           =10x26
           =260
ezzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz}}

a) 13 x 5 x 2

= 13 x (5 x 2)

= 13 x 10 = 130

5 x 2 x 34

= (5 x 2 ) x 34

= 10 x 34 = 340

b) 2 x 26 x 5

= 26 x (2 x 5)

= 26 x 10 = 260

5 x 9 x 3 x 2

= (9 x 3) x (5 x 2)

= 27 x 10 = 270

          234 x 13 + 234 x 87 = 234 x (13 + 87)

                               = 234 x 100

                               = 23 400

tính bang cách thuận tiện: 735-48-35

234 x 13 + 234 x 87

=234 x (13+87)

=234 x 100

=23400