$\text{Bài 1}$

$a,$ $\dfrac{3}{5}$ $+$ $\dfrac{4}{5}$

$=$ $\dfrac{9}{15}$ $+$ $\dfrac{4}{5}$

$=$ $\dfrac{13}{15}$

$b,$ $\dfrac{37}{60}$ $-$ $\dfrac{2}{15}$

$=$ $\dfrac{37}{60}$ $-$ $\dfrac{8}{60}$

$=$ $\dfrac{29}{60}$

$c,$ $\dfrac{3}{8}$ $×$ $\dfrac{11}{12}$

$=$ $\dfrac{3 × 11}{8 × 12}$

$=$ $\dfrac{33}{96}$

$=$ $\dfrac{11}{32}$

$d,$ $\dfrac{7}{9}$ $÷$ $\dfrac{2}{3}$

$=$ $\dfrac{7}{9}$ × $\dfrac{3}{2}$

$=$ $\dfrac{21}{18}$

$=$ $\dfrac{7}{6}$

$\text{Bài 2}$

$a,$ $\dfrac{1}{7}$ $+ x =$ $\dfrac{7}{8}$

                              $x =$ $\dfrac{7}{8}$ - $\dfrac{1}{7}$

                              $x =$ $\dfrac{41}{56}$

$b,x ×$ $\dfrac{3}{4}$ $=$ $\dfrac{2}{5}$

                     $x =$ $\dfrac{2}{5}$ $÷$ $\dfrac{3}{4}$

                     $x =$ $\dfrac{8}{15}$

$c,x +$ $\dfrac{1}{9}$ $=$ $\dfrac{1}{3}$

                      $x =$ $\dfrac{1}{3}$ $-$ $\dfrac{1}{9}$

                      $x =$ $\dfrac{2}{9}$
$@anhvu19120122$

 

Bài `1`:

`c) 3/8×11/12= (3×11)/(8×12)= 11/32`

`d) 7/9:2/3= 7/9×3/2= (7×3)/(9×2)= 7/6`

Bài `2`:

`a) 1/7+x= 7/8`

            `x= 7/8-1/7`

            `x= 41/56`

`b) x×3/4= 2/5`

    `x= 2/5:3/4`

    `x= 8/15`