Đáp án:

 $1) \dfrac{x}{6} = \dfrac{8}{3}$

$ ⇒ x = \dfrac{6.8}{3}$

$⇒ x = 16$

$2)\dfrac{x}{6} = \dfrac{7}{4}$

$⇒x = \dfrac{6.7}{4}$

$⇒x = 10,5$

$3) \dfrac{x}{3} = \dfrac{5}{24}$

$⇒ x = \dfrac{3.5}{24}$

$⇒ x = 0,625$

$4)\dfrac{3}{x} = \dfrac{21}{17}$

$⇒ x= \dfrac{3.17}{21}$

$⇒ x = \dfrac{17}{7}$

$5)\dfrac{125}{x} = \dfrac{25}{3}$

$⇒ x = \dfrac{125.3}{25}$

$⇒ x= 15$

$6) \dfrac{-3}{x} = \dfrac{15}{7}$

$⇒ x = \dfrac{-3.7}{15}$

$⇒ x= -1,4$

$7)\dfrac{0,1}{5} = \dfrac{x}{15}$

$⇒x = \dfrac{15.0,1}{5}$

$⇒x = 0,3$

$8)\dfrac{-4}{1,2} = \dfrac{x}{-3,6}$

$⇒ x = \dfrac{-3,6 . (-4)}{1,2}$

$⇒ x = 12$

$9) \dfrac{-2,6}{12} = \dfrac{x}{-42}$

$⇒ x = \dfrac{-42 . (-2,6)}{12}$

$⇒ x = 9,1$

$10) \dfrac{21}{14} = \dfrac{33}{x}$

$⇒ x = \dfrac{33.14}{21}$

$⇒ x= 22$

$11) \dfrac{1,4}{-5} = \dfrac{2,1}{x}$

$⇒ x= \dfrac{2,1 . (-5)}{1,4}$

$⇒ x= -7,5$

$12) \dfrac{0,12}{3} = \dfrac{0,21}{x}$

$⇒ x = \dfrac{0,21.3}{0,12}$

$⇒ x = 5,25$

$13) \dfrac{x-2}{3} = \dfrac{4}{5}$

$⇒ \dfrac{5(x-2)}{15}$ = \dfrac{12}{15}$

$⇒ 5(x-2)= 12$

$⇒ 5x -10 = 12$

$ ⇒ 5x = 22$

$⇒ x = \dfrac{22}{5}$

$14) \dfrac{x+3}{-4} = \dfrac{5}{20}$

$⇒ \dfrac{-5(x+3)}{20} = \dfrac{5}{20}$

$⇒ -5(x+3) = 5$

$⇒ -5x -15 =5$

$⇒ -5x = 20$

$⇒ x = 20 : (-5)$

$⇒ x = -4$

$15) \dfrac{3}{x-1} =\dfrac{21}{16}$

ĐKXĐ : x $\neq$ 1

$⇒ \dfrac{48}{16(x-1)} = \dfrac{21(x-1)}{16(x-1)}$

$⇒ 48 = 21(x-1)$

$⇒ 48 = 21x -21$

$⇒ -21x= -21 -48$

$ ⇒ -21x = -69$

$⇒ x = -69 : (-21)$

$⇒ x = \dfrac{23}{7}$(thỏa mãn)

16 ) \dfrac{52}{2x-1} = \dfrac{13}{30}$

ĐKXĐ : x $\neq$ $\dfrac{1}{2}$

$⇒ \dfrac{1560}{30(2x-1)} = \dfrac{13(2x-1)}{30(2x-1)}$

$⇒ 1560 = 13(2x-1)$

$⇒ 1560 = 26x -13$

$⇒ -26x = -13 - 1560$

$⇒ -26x = -1573$

$⇒ x = -1573 : (-26)$

$⇒ x = 60,5$(thỏa mãn)

$1$) $\dfrac{x}{6} = \dfrac{8}{3}$

$⇔ x = 48 : 3$

$⇔ x = 16$

   Vậy $x=16$

$2$) $\dfrac{x}{6} = \dfrac{7}{4}$

$⇔  x = 42 : 4$

$⇔ x = 10,5$

   Vậy $x=10,5$

$3$) $\dfrac{x}{3} = \dfrac{5}{24}$

$⇔ x = 15 : 24$

$⇔ x = 0,625$

   Vậy $x=0,625$

$4$) `3/x = 21/17`

`⇔ x = 51 :21`

`⇔ x = 17/7`

   Vậy `x=17/7`

$5$) `125/x = 25/3`

`⇔ x = 15`

   Vậy `x=15`

$6$) `-3/x = 15/7`

`⇔ x = -21/15`

`⇔ x = -1,4`

   Vậy `x=-1,4` 

$7$) $\dfrac{0,1}{5} = \dfrac{x}{15}$

`⇔ 1,5 = 5x`

`⇔ x = 0,3`

   Vậy $x=0,3$

$8$) $\dfrac{-4}{1,2} = \dfrac{x}{-3,6}$

$⇔ -4.(-3,6) = 1,2x$

$⇔ 14,4 = 1,2x$

$⇔ x = 12$

   Vậy $x=12$

$9$) $\dfrac{-2,6}{12} = \dfrac{x}{-42}$

$⇔ -2,6 . (-42) = 12x$

$⇔ 109,2 = 12x$

$⇔ x = 9,1$

   Vậy $x=9,1$

$10$) `21/14 = 33/x`

`⇔ x = 462 : 21`

`⇔ x = 22`

   Vậy `x=22`

$11$) $\dfrac{1,4}{-5} = \dfrac{2,1}{x}$

$⇔ 1,4x = -10,5$

$⇔ x = -7,5$

   Vậy $x = -7,5$

$12$) $\dfrac{0,12}{3} = \dfrac{0,21}{x}$

$⇔ 0,12x = 0,63$

$⇔ x = 5,25$

   Vậy $x=5,25$

$13$) `{x-2}/3 = 4/5`

`⇔ 5x - 10 = 12`

`⇔ 5x = 22`

`⇔ x = 4,4`

    Vậy `x=4,4`

$14$) $\dfrac{x+3}{-4} = \dfrac{5}{20}$

$⇔ 20x + 60 = -20$

$⇔ 20x = -80$

$⇔ x = -4$

   Vậy $x=-4$

$15$) `3/{x-1} = 21/16`

`⇔ x-1 = 48 : 21`

`⇔ x-1 = 16/7`

`⇔ x = 23/7`

   Vậy `x=23/7`

$16$) $\dfrac{52}{2x-1} = \dfrac{13}{30}$

$⇔ \dfrac{52}{2x-1} = \dfrac{52}{120}$

$⇔ 2x-1 = 120$

$⇔ x = 60,5$

   Vậy $x=60,5$