Bài `3:`

`a)` $\dfrac{5}{9}$`+`$\dfrac{2}{3}$

`=`$\dfrac{5}{9}$`+`$\dfrac{6}{9}$

`=`$\dfrac{11}{9}$

`b)` $\dfrac{7}{8}$`xx`$\dfrac{5}{7}$

`=`$\dfrac{7×5}{8×7}$

`=`$\dfrac{5}{8}$

`c)` $\dfrac{2}{3}$`xx`$\dfrac{3}{4}$`-`$\dfrac{1}{3}$

`=`$\dfrac{1}{2}$`-`$\dfrac{1}{3}$

`=`$\dfrac{3}{6}$`-`$\dfrac{2}{6}$

`=`$\dfrac{1}{6}$

Bài `4:`

`a)` `x+`$\dfrac{4}{7}$`=`$\dfrac{5}{6}$

`x=`$\dfrac{5}{6}$`-`$\dfrac{4}{7}$

`x=`$\dfrac{11}{42}$

`b)` $\dfrac{3}{4}$`-x=`$\dfrac{7}{12}$

`x=`$\dfrac{3}{4}$`-`$\dfrac{7}{12}$

`x=`$\dfrac{1}{6}$

Đáp án + Giải thích các bước giải :

Bài 3 :

a) $\frac{5}{9}$ x$\frac{2}{3}$ =$\frac{10}{27}$ 

b) $\frac{7}{8}$ x$\frac{5}{7}$ =$\frac{35}{56}$ 

c) $\frac{2}{3}$ x$\frac{3}{4}$- $\frac{1}{3}$ =$\frac{6}{12}$ -$\frac{1}{3}$ =$\frac{6}{12}$ -$\frac{6}{12}$ -$\frac{4}{12}$ =$\frac{2}{12}$ =$\frac{1}{6}$ 

Bài 4 :

a) x + $\frac{4}{7}$ =$\frac{5}{6}$ 

                x = $\frac{35}{42}$ +$\frac{24}{42}$ 

                x = $\frac{59}{42}$ 

b) $\frac{3}{4}$ - x = $\frac{7}{12}$ 

                           x = $\frac{9}{12}$ - $\frac{7}{12}$ 

                          x = $\frac{2}{12}$ =$\frac{1}{6}$ 

Bài 5 :

a)       576402

+

_______285694____

          862096

Vậy 576402 + 285694 = 862096

___________________________________

b)         649072

_

________178526______

            470546

Vậy 649072 - 178526 = 470546

___________________________________

c)              1334

x

____________376_______

                 8004

               9338

             4002

            501584

Vậy 1334 x 376 = 501584

_____________________________

d) 5867 |___17___

       76  | 345

         87

           2

Vậy 5867 : 17 = 345 ( dư 2 )

$\text{hoidap247loc}$