a) \(\frac{\frac{2}{3}+\frac{2}{7}-\frac{1}{14}}{-1\frac{3}{7}+\frac{3}{28}}\)

= \(\frac{\frac{28}{42}+\frac{12}{42}-\frac{3}{42}}{\frac{-10}{7}+\frac{3}{28}}\)

= \(\frac{\frac{37}{42}}{\frac{-40}{28}+\frac{3}{28}}\)

= \(\frac{\frac{37}{42}}{\frac{-37}{28}}\)

= \(\frac{37}{42}.\frac{-28}{37}\)

= \(\frac{-3}{2}\)

b) `(3\frac{3}{5}-2\frac{2}{5}).\frac{-5}{3}+3.(2\frac{1}{2}:\frac{1}{2})`

`= (\frac{18}{5}-\frac{12}{5}).\frac{-5}{3}+3.(\frac{5}{2}.2)`

`=\frac{6}{5}.\frac{-5}{3}+3.5`

`=-2+15`

`=13`

c) `\frac{28.7-45.7+7.18}{45.14}`

`=\frac{7(28-45+18)}{45.14}`

`=\frac{7.1}{45.14}`

`=\frac{1}{90}`

Bài 2:

a) `30%.x=0,6`

`\frac{3}{10}.x=\frac{3}{5}`

`x=\frac{3}{5}:\frac{3}{10}`

`x=\frac{3}{5}.\frac{10}{3}`

`x=2`

b) `\frac{2}{3}.(\frac{1}{2}-x)=\frac{5}{6}`

`\frac{1}{3}-\frac{2}{3}x=\frac{5}{6}`

`-\frac{2}{3}x=\frac{1}{2}`

`-\frac{2}{3}x=\frac{5}{6}`

`x=\frac{-3}{4}`

c) `2x:3\frac{1}{4}=0,5`

`2x:\frac{13}{4}=\frac{1}{2}`

`2x=\frac{1}{2}.\frac{13}{4}`

`2x=\frac{13}{8}`

`x=\frac{13}{16}`

Bài 3: 

a) Đóng được số chai là:

`300:\frac{3}{4}=400\ \text{chai}`

b) Cần số hộp để xếp đủ số chai nước khoáng nói trên là:

`400:25=16\ \text{hộp}`

`a, (2/3+2/7-1/14)/(-1 3/7 + 3/28)=(28/42+12/42-3/42)/((-10)/7+3/28)=(37/42)/((-40)/28+3/28)`

`=(37/42)/((-37)/28)=37/42 : (-37)/28=37/42 . (-28)/37=-2/3`

`b,(3 3/5 - 2 2/5) . (-5)/3 + 3(2 1/2 : 1/2)`

`=(3,6-2,4).(-5)/3+3(2,5.2)`

`=1,2.(-5)/3+3.5=-2+15=13`

`c, (28.7-45.7+7.18)/(45.14)`

`=(7.(28-45+18))/(45.2.7)`

`=(7.1)/(90.7)=1/90`

`......`

`a, 30%x=0,6`

`⇒ 3/10 x = 0,6`

`⇒ x = 0,6 : 3/10`

`⇒ x = 0,6 . 10/3`

`⇒ x = 2`

`b, 2/3 (1/2 -x) = 5/6`

`⇒ 2/6 - 2/3 x = 5/6`

`⇒ 2/3 x = 2/6 - 5/6`

`⇒ 2/3 x = (-1)/2`

`⇒ x = (-1)/2 : 2/3`

`⇒ x = (-1)/2 . 3/2`

`⇒ x = (-3)/4`

`c, 2x : 3 1/4 = 0,5`

`⇒ 2x : 3,25 =0,5`

`⇒ 2x = 0,5 . 3,25`

`⇒ 2x = 1,625`

`⇒ x = 0,8125`

`......`

$\text{a, Đóng được số chai là:}$

`300:3/4=400(chai)`

$\text{b, Để xếp đủ số chai nước khoáng nói trên cần số hộp là:}$

`400:25=16(hộp)`